Changed default to per-TU violation handlers

And removed the feature test macro to instead tgest for a specific C++ version.

.gitattributes

@@ -1 +0,0 @@
-include/gsl/* linguist-language=C++

.github/workflows/android.yml

@@ -1,9 +1,9 @@
 name: CI_Android
 on:
   push:
-    branches: [ main ]
+    branches: [ master ]
   pull_request:
-    branches: [ main ]
+    branches: [ master ]
 
 jobs:
   Android:
@@ -29,7 +29,7 @@ jobs:
           echo "Emulator starting"
 
       - name: Configure
-        run: cmake -Werror=dev -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_LATEST_HOME/build/cmake/android.toolchain.cmake -DANDROID_PLATFORM=16 -DANDROID_ABI=x86_64 -DCMAKE_BUILD_TYPE=Debug ..
+        run: cmake -DCMAKE_TOOLCHAIN_FILE=$ANDROID_HOME/ndk-bundle/build/cmake/android.toolchain.cmake -DANDROID_PLATFORM=16 -DANDROID_ABI=x86_64 -DCMAKE_BUILD_TYPE=Debug ..
 
       - name: Build
         run: cmake --build . --parallel
@@ -47,4 +47,4 @@ jobs:
           adb shell find /data/local/tmp/tests -maxdepth 1 -exec chmod +x {} \\\;
 
       - name: Test
-        run: adb shell find /data/local/tmp/tests -name "*_tests" -maxdepth 1 -exec {} \\\;
+        run: adb shell find /data/local/tmp/tests -name "*_tests" -maxdepth 1 -exec {} \\\;

.github/workflows/cmake_find_package.yml

@@ -1,25 +0,0 @@
-name: cmake_find_package
-on:
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
-
-jobs:
-  cmake-find-package:
-    name: Build ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      matrix:
-        os: [ ubuntu-latest, macos-latest ]
-    steps:
-      - uses: actions/checkout@v3
-      - uses: lukka/get-cmake@latest
-        with:
-          cmakeVersion: 3.14.0
-      - name: Configure GSL
-        run: cmake -S . -B build -G "Ninja" -D GSL_TEST=OFF -D CMAKE_INSTALL_PREFIX=${GITHUB_WORKSPACE}/build/install
-      - name: Install GSL
-        run: cmake --build build --target install
-      - name: Test GSL find_package support
-        run: cmake -S tests/ -B build/tests_find_package -G "Ninja" -D CMAKE_PREFIX_PATH=${GITHUB_WORKSPACE}/build/install -D CMAKE_BUILD_TYPE=Release

.github/workflows/ios.yml

@@ -1,9 +1,9 @@
 name: CI_iOS
 on:
   push:
-    branches: [ main ]
+    branches: [ master ]
   pull_request:
-    branches: [ main ]
+    branches: [ master ]
 
 jobs:
   iOS:
@@ -21,15 +21,14 @@ jobs:
       - name: Configure
         run: |
           cmake \
-            -Werror=dev \
             -GXcode \
             -DCMAKE_SYSTEM_NAME=iOS \
             "-DCMAKE_OSX_ARCHITECTURES=arm64;x86_64" \
-            -DCMAKE_OSX_DEPLOYMENT_TARGET=9 \
+            -DCMAKE_OSX_DEPLOYMENT_TARGET=8 \
             -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY \
             "-DMACOSX_BUNDLE_GUI_IDENTIFIER=GSL.\$(EXECUTABLE_NAME)" \
-            -DMACOSX_BUNDLE_BUNDLE_VERSION=3.1.0 \
-            -DMACOSX_BUNDLE_SHORT_VERSION_STRING=3.1.0 \
+            -DMACOSX_BUNDLE_BUNDLE_VERSION=3.0.1 \
+            -DMACOSX_BUNDLE_SHORT_VERSION_STRING=3.0.1 \
             ..
 
       - name: Build

.travis.yml

@@ -0,0 +1,337 @@
+
+language: cpp
+notifications:
+  email: false
+
+# Use Linux unless specified otherwise
+os: linux
+dist: bionic
+
+cache:
+  directories:
+    - ${TRAVIS_BUILD_DIR}/deps
+
+stages:
+  - name: Latest     # Compiler with the latest major version
+  - name: Previous   # Compilers with the major version Latest - 1
+  - name: Validation # run other jobs
+
+jobs:
+  include:
+
+    ##########################################################################
+    # Validate CMake configuration
+    ##########################################################################
+
+    - name: CMake 3.1.3 - latest
+      stage: Validation
+      env: &CMAKE_VERSION_LIST
+      - CMAKE_VERSION: '"3.17.0 3.16.5 3.15.7 3.14.7 3.13.5 3.12.4 3.11.4 3.10.3 3.9.6 3.8.2 3.7.2 3.6.3 3.5.2 3.4.3 3.3.2 3.2.3 3.1.3"'
+      - GSL_CXX_STANDARD: 14
+      addons: # Get latest release (candidate)
+        apt:
+          sources:
+          - sourceline: 'deb https://apt.kitware.com/ubuntu/ bionic main'
+            key_url: 'https://apt.kitware.com/keys/kitware-archive-latest.asc'
+          - sourceline: 'deb https://apt.kitware.com/ubuntu/ bionic-rc main'
+          packages:
+          - cmake
+      script:
+      - |
+        cd ./build
+        ( set -eu
+          for CMAKE in ${CMAKE_path[@]}; do test_CMake_generate $CMAKE; done
+          export CXX=clang++
+          for CMAKE in ${CMAKE_path[@]}; do test_CMake_generate $CMAKE; done
+        )
+
+    - name: CMake 3.2.3 - 3.17.0
+      stage: Validation
+      os: osx
+      osx_image: xcode11.3
+      env:
+      - CMAKE_VERSION: '"3.17.0 3.16.5 3.15.7 3.14.7 3.13.5 3.12.4 3.11.4 3.10.3 3.9.6 3.8.2 3.7.2 3.6.3 3.5.2 3.4.3 3.3.2 3.2.3"'
+      script:
+      - |
+        cd ./build
+        ( set -eu
+          for CMAKE in ${CMAKE_path[@]}; do test_CMake_generate $CMAKE; done
+        )
+
+    ##########################################################################
+    # AppleClang on OSX
+    ##########################################################################
+
+
+
+    # Xcode 10.3
+    - name: AppleClang Xcode-10.3 C++14 Debug
+      stage: Previous
+      env: BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      os: osx
+      osx_image: xcode10.3 # AppleClang 10.0.1 same compiler as Xcode 10.2
+    - name: AppleClang Xcode-10.3 C++14 Release
+      env: BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      os: osx
+      osx_image: xcode10.3
+    - name: AppleClang Xcode-10.3 C++17 Debug
+      env: BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      os: osx
+      osx_image: xcode10.3
+    - name: AppleClang Xcode-10.3 C++17 Release
+      env: BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      os: osx
+      osx_image: xcode10.3
+
+
+    # Xcode 11.4
+    - name: AppleClang Xcode-11.4 C++17 Debug
+      stage: Latest
+      env: BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      os: osx
+      osx_image: xcode11.4
+    - name: AppleClang Xcode-11.4 C++17 Release
+      env: BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      os: osx
+      osx_image: xcode11.4
+    - name: AppleClang Xcode-11.4 C++14 Debug
+      env: BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      os: osx
+      osx_image: xcode11.4
+    - name: AppleClang Xcode-11.4 C++14 Release
+      env: BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      os: osx
+      osx_image: xcode11.4
+
+    ##########################################################################
+    # Clang on Linux
+    ##########################################################################
+
+    # Clang 9
+    - name: Clang-9 C++14 Debug
+      stage: Previous
+      env: CXX=clang++-9 BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      addons: &clang9
+        apt:
+          sources:
+          - sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
+            key_url: https://apt.llvm.org/llvm-snapshot.gpg.key
+          packages:
+          - clang-9
+    - name: Clang-9 C++14 Release
+      env: CXX=clang++-9 BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      addons: *clang9
+    - name: Clang-9 C++17 Debug
+      env: CXX=clang++-9 BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      addons: *clang9
+    - name: Clang-9 C++17 Release
+      env: CXX=clang++-9 BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      addons: *clang9
+
+    # Clang 10
+    - name: Clang-10 C++14 Debug
+      stage: Latest
+      env: CXX=clang++-10 BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      addons: &clang10
+        apt:
+          sources:
+          - sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main'
+            key_url: https://apt.llvm.org/llvm-snapshot.gpg.key
+          packages:
+          - clang-10
+    - name: Clang-10 C++14 Release
+      env: CXX=clang++-10 BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      addons: *clang10
+    - name: Clang-10 C++17 Debug
+      env: CXX=clang++-10 BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      addons: *clang10
+    - name: Clang-10 C++17 Release
+      env: CXX=clang++-10 BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      addons: *clang10
+
+    ##########################################################################
+    # GCC on Linux
+    ##########################################################################
+
+    # GCC 8
+    - name: GCC-8 C++14 Debug
+      stage: Previous
+      env: CXX=g++-8 BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      addons: &gcc8
+        apt:
+          packages: g++-8
+    - name: GCC-8 C++14 Release
+      env: CXX=g++-8 BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      addons: *gcc8
+    - name: GCC-8 C++17 Debug
+      env: CXX=g++-8 BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      addons: *gcc8
+    - name: GCC-8 C++17 Release
+      env: CXX=g++-8 BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      addons: *gcc8
+
+    # GCC 9
+    - name: GCC-9 C++14 Debug
+      stage: Latest
+      env: CXX=g++-9 BUILD_TYPE=Debug GSL_CXX_STANDARD=14
+      addons: &gcc9
+        apt:
+          sources:
+          - sourceline: ppa:ubuntu-toolchain-r/test
+          packages:
+          - g++-9
+    - name: GCC-9 C++14 Release
+      env: CXX=g++-9 BUILD_TYPE=Release GSL_CXX_STANDARD=14
+      addons: *gcc9
+    - name: GCC-9 C++17 Debug
+      env: CXX=g++-9 BUILD_TYPE=Debug GSL_CXX_STANDARD=17
+      addons: *gcc9
+    - name: GCC-9 C++17 Release
+      env: CXX=g++-9 BUILD_TYPE=Release GSL_CXX_STANDARD=17
+      addons: *gcc9
+
+before_install:
+  - |
+    # Configuration
+    JOBS=2 # Travis machines have 2 cores
+    # Dependencies required by the CI (cached directory)
+    DEPS_DIR="${TRAVIS_BUILD_DIR}/deps"
+  - |
+    # Setup
+    mkdir -p "${DEPS_DIR:?}" && cd "${DEPS_DIR:?}"
+    mkdir -p ~/tools && cd ~/tools
+    if [[ ${TRAVIS_OS_NAME:?} == "osx" ]]; then
+      export PATH="/usr/local/opt/coreutils/libexec/gnubin:$PATH"
+    fi
+  - |
+    # Helper functions
+    # usage: if [[ $(check_url '<url>') ]]; then ...
+    function check_url {( set +e
+      if [[ "$1" =~ 'github.com' ]]; then # check for first byte
+        if curl --fail --silent --output /dev/null --connect-timeout 12 --range 0-0 "$1"
+        then echo true; fi
+      else # request head
+        if curl --fail --silent --output /dev/null --connect-timeout 12 --head "$1"
+        then echo true; fi
+      fi
+      return
+    )}
+
+install:
+  ############################################################################
+  # Install a different CMake version (or several)
+  ############################################################################
+  - |
+    # Install CMake versions
+    ( set -euo pipefail
+      if [[ ${CMAKE_VERSION:-} ]]; then
+        if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+          OS="Linux"; EXT="sh"
+          if [[ ! ("${CMAKE_VERSION:-}" =~ .+[' '].+) ]]; then
+            # Single entry -> default CMake version
+            CMAKE_DEFAULT_DIR="/usr/local"
+          fi
+        elif [[ "${TRAVIS_OS_NAME}" == "osx" ]]; then OS="Darwin"; EXT="tar.gz"
+        else echo "CMake install not supported for this OS."; exit 1
+        fi
+        CMAKE_INSTALLER="install-cmake.${EXT}"
+      fi
+      for VERSION in ${CMAKE_VERSION:-}; do
+        CMAKE_URL="https://github.com/Kitware/CMake/releases/download/v${VERSION}/cmake-${VERSION}-${OS}-x86_64.${EXT}"
+        if [[ $(check_url "$CMAKE_URL") ]]; then
+          curl -sSL ${CMAKE_URL} -o ${CMAKE_INSTALLER}
+          CMAKE_DIR="${CMAKE_DEFAULT_DIR:-"${HOME}/tools/cmake-${VERSION}"}"
+          mkdir -p ${CMAKE_DIR}
+          if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+            chmod +x ${CMAKE_INSTALLER}
+            sudo ./${CMAKE_INSTALLER} --prefix=${CMAKE_DIR} --skip-license
+          else # OSX
+            mkdir -p ./CMake_tmp
+            tar --extract --gzip --file=${CMAKE_INSTALLER} --directory=./CMake_tmp
+            mv ./CMake_tmp/*/CMake.app/Contents/* ${CMAKE_DIR}
+          fi
+          rm --recursive --force ./CMake_tmp ${CMAKE_INSTALLER}
+        else echo 'Invalid url!'; echo "Version: ${VERSION}"
+        fi
+      done
+    )
+    if [[ ${CMAKE_VERSION:-} && "${TRAVIS_OS_NAME:?}" == "osx" && ! ("${CMAKE_VERSION:-}" =~ .+[' '].+) ]]
+    then # Single entry -> default CMake version
+      export PATH=${HOME}/tools/cmake-${CMAKE_VERSION:?}/bin:$PATH
+    fi
+    CMAKE_path=("cmake") # start with installed CMake version
+    for VERSION in ${CMAKE_VERSION:-}; do
+      tmp_path="$HOME/tools/cmake-${VERSION:?}/bin/cmake"
+      if [[ -x "$(command -v ${tmp_path:?})" ]]; then CMAKE_path+=("${tmp_path:?}"); fi
+    done
+    function test_CMake_generate {
+      # $1: cmake or full path to cmake
+      shopt -s extglob
+      if [[ "$1" == "cmake" || -x "$(command -v $1)" && "$1" =~ .*cmake$ ]]; then
+        echo "----------------"
+        $1 --version
+        echo "Configuration = ${BUILD_TYPE:-Debug}"
+        $1 -DCMAKE_BUILD_TYPE=${BUILD_TYPE:-Debug} ${CMAKE_GEN_FLAGS[@]:?} ..
+        rm -rf !(tests/googletest-*)
+        if [[ ! ${BUILD_TYPE:-} ]]; then echo "" && echo "Configuration = Release"
+          $1 -DCMAKE_BUILD_TYPE=Release ${CMAKE_GEN_FLAGS[@]:?} ..
+          rm -rf !(tests/googletest-*)
+        fi
+      else echo "Non existing command: $1"
+      fi
+    }
+  - |
+    # CMake wrapper (Trusty, Xenial & Bionic); restore default behaviour.
+    if [[ "${TRAVIS_OS_NAME:?}" == "linux" &&
+          "$(lsb_release --codename)" =~ (trusty|xenial|bionic)$ ]]
+    then
+      if [[ -x $(command -v /usr/local/bin/cmake) ]]; then
+        function cmake { command /usr/local/bin/cmake $@; }
+      elif [[ -x $(command -v /usr/bin/cmake) ]]; then
+        function cmake { command /usr/bin/cmake $@; }
+      fi
+    fi
+
+  ############################################################################
+  # [linux]: Install the right version of libc++
+  # Based on https://github.com/ldionne/hana/blob/master/.travis.yml
+  ############################################################################
+  - |
+    LLVM_INSTALL=${DEPS_DIR:?}/llvm/install
+    # if in linux and compiler clang and llvm not installed
+    if [[ "${TRAVIS_OS_NAME:?}" == "linux" && "${CXX%%+*}" == "clang" && -n "$(ls -A ${LLVM_INSTALL:?})" ]]; then
+      if   [[ "${CXX}" == "clang++-3.6" ]]; then LLVM_VERSION="3.6.2";
+      elif [[ "${CXX}" == "clang++-3.7" ]]; then LLVM_VERSION="3.7.1";
+      elif [[ "${CXX}" == "clang++-3.8" ]]; then LLVM_VERSION="3.8.1";
+      elif [[ "${CXX}" == "clang++-3.9" ]]; then LLVM_VERSION="3.9.1";
+      fi
+      LLVM_URL="http://llvm.org/releases/${LLVM_VERSION}/llvm-${LLVM_VERSION}.src.tar.xz"
+      LIBCXX_URL="http://llvm.org/releases/${LLVM_VERSION}/libcxx-${LLVM_VERSION}.src.tar.xz"
+      LIBCXXABI_URL="http://llvm.org/releases/${LLVM_VERSION}/libcxxabi-${LLVM_VERSION}.src.tar.xz"
+      mkdir -p llvm llvm/build llvm/projects/libcxx llvm/projects/libcxxabi
+      travis_retry wget -O - ${LLVM_URL} | tar --strip-components=1 -xJ -C llvm
+      travis_retry wget -O - ${LIBCXX_URL} | tar --strip-components=1 -xJ -C llvm/projects/libcxx
+      travis_retry wget -O - ${LIBCXXABI_URL} | tar --strip-components=1 -xJ -C llvm/projects/libcxxabi
+      (cd llvm/build && cmake .. -DCMAKE_INSTALL_PREFIX=${LLVM_INSTALL})
+      (cd llvm/build/projects/libcxx && make install -j2)
+      (cd llvm/build/projects/libcxxabi && make install -j2)
+      export CXXFLAGS="-isystem ${LLVM_INSTALL}/include/c++/v1"
+      export LDFLAGS="-L ${LLVM_INSTALL}/lib -l c++ -l c++abi"
+      export LD_LIBRARY_PATH="${LD_LIBRARY_PATH}:${LLVM_INSTALL}/lib"
+    fi
+
+before_script:
+  - |
+    cd "${TRAVIS_BUILD_DIR:?}"
+    mkdir build && cd build
+    if [[ ${GSL_CXX_STANDARD:-} ]]; then
+      CMAKE_GEN_FLAGS=("-DGSL_CXX_STANDARD=$GSL_CXX_STANDARD")
+    fi
+    CMAKE_GEN_FLAGS+=("-Wdev -Werror=dev --warn-uninitialized")
+
+script:
+  # generate build files
+  - cmake .. -DCMAKE_BUILD_TYPE=${BUILD_TYPE:?} ${CMAKE_GEN_FLAGS[@]:?}
+  # build and run tests
+  - cmake --build . -- -j${JOBS}
+  - ctest --output-on-failure -j${JOBS}

CMakeLists.txt

@@ -1,48 +1,117 @@
-cmake_minimum_required(VERSION 3.14...3.16)
+cmake_minimum_required(VERSION 3.1.3...3.16)
 
-project(GSL VERSION 4.0.0 LANGUAGES CXX)
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/")
+include(guidelineSupportLibrary)
 
+project(GSL VERSION 3.1.0 LANGUAGES CXX)
+
+include(ExternalProject)
+find_package(Git)
+
+# Use GNUInstallDirs to provide the right locations on all platforms
+include(GNUInstallDirs)
+
+# Creates a library GSL which is an interface (header files only)
 add_library(GSL INTERFACE)
+
+# NOTE: If you want to use GSL prefer to link against GSL using this alias target
+# EX:
+#   target_link_libraries(foobar PRIVATE Microsoft.GSL::GSL)
+#
+# Add Microsoft.GSL::GSL alias for GSL so that dependents can be agnostic about
+# whether GSL was added via `add_subdirectory` or `find_package`
 add_library(Microsoft.GSL::GSL ALIAS GSL)
 
-# https://cmake.org/cmake/help/latest/variable/PROJECT_IS_TOP_LEVEL.html
-string(COMPARE EQUAL ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_SOURCE_DIR} PROJECT_IS_TOP_LEVEL)
+# Determine whether this is a standalone project or included by other projects
+set(GSL_STANDALONE_PROJECT OFF)
+if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
+    set(GSL_STANDALONE_PROJECT ON)
+endif()
 
-option(GSL_INSTALL "Generate and install GSL target" ${PROJECT_IS_TOP_LEVEL})
-option(GSL_TEST "Build and perform GSL tests" ${PROJECT_IS_TOP_LEVEL})
+# This GSL implementation generally assumes a platform that implements C++14 support.
+set(gsl_min_cxx_standard "14")
 
-# The implementation generally assumes a platform that implements C++14 support
-target_compile_features(GSL INTERFACE "cxx_std_14")
+if (GSL_STANDALONE_PROJECT)
+    gsl_set_default_cxx_standard(${gsl_min_cxx_standard})
+else()
+    gsl_client_set_cxx_standard(${gsl_min_cxx_standard})
+endif()
 
-# Setup include directory
-add_subdirectory(include)
+# add definitions to the library and targets that consume it
+target_compile_definitions(GSL INTERFACE
+    $<$<CXX_COMPILER_ID:MSVC>:
+        # remove unnecessary warnings about unchecked iterators
+        _SCL_SECURE_NO_WARNINGS
+        # remove deprecation warnings about std::uncaught_exception() (from catch)
+        _SILENCE_CXX17_UNCAUGHT_EXCEPTION_DEPRECATION_WARNING
+    >
+)
 
-target_sources(GSL INTERFACE $<BUILD_INTERFACE:${GSL_SOURCE_DIR}/GSL.natvis>)
+# add include folders to the library and targets that consume it
+# the SYSTEM keyword suppresses warnings for users of the library
+if(GSL_STANDALONE_PROJECT)
+    target_include_directories(GSL INTERFACE
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+    )
+else()
+    target_include_directories(GSL SYSTEM INTERFACE
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+    )
+endif()
 
+
+if (CMAKE_VERSION VERSION_GREATER 3.7.8)
+    if (MSVC_IDE)
+        option(GSL_VS_ADD_NATIVE_VISUALIZERS "Configure project to use Visual Studio native visualizers" TRUE)
+    else()
+        set(GSL_VS_ADD_NATIVE_VISUALIZERS FALSE CACHE INTERNAL "Native visualizers are Visual Studio extension" FORCE)
+    endif()
+
+    # add natvis file to the library so it will automatically be loaded into Visual Studio
+    if(GSL_VS_ADD_NATIVE_VISUALIZERS)
+        target_sources(GSL INTERFACE
+            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/GSL.natvis>
+        )
+    endif()
+endif()
+
+install(TARGETS GSL EXPORT Microsoft.GSLConfig)
+install(
+    DIRECTORY include/gsl
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+)
+# Make library importable by other projects
+install(EXPORT Microsoft.GSLConfig NAMESPACE Microsoft.GSL:: DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
+export(TARGETS GSL NAMESPACE Microsoft.GSL:: FILE Microsoft.GSLConfig.cmake)
+
+# Add find_package() versioning support. The version for
+# generated Microsoft.GSLConfigVersion.cmake will be used from
+# last project() command. The version's compatibility is set between all
+# minor versions (as it was in prev. GSL releases).
+include(CMakePackageConfigHelpers)
+if(${CMAKE_VERSION} VERSION_LESS "3.14.0")
+    write_basic_package_version_file(
+        ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
+        COMPATIBILITY SameMajorVersion
+    )
+else()
+    write_basic_package_version_file(
+        ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
+        COMPATIBILITY SameMajorVersion
+        ARCH_INDEPENDENT
+    )
+endif()
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
+
+option(GSL_TEST "Generate tests." ${GSL_STANDALONE_PROJECT})
 if (GSL_TEST)
     enable_testing()
+    if(IOS)
+        add_compile_definitions(
+            GTEST_HAS_DEATH_TEST=1
+        )
+    endif()
     add_subdirectory(tests)
-endif()
-
-if (GSL_INSTALL)
-    include(GNUInstallDirs)
-    include(CMakePackageConfigHelpers)
-
-    install(DIRECTORY "${PROJECT_SOURCE_DIR}/include/gsl" DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
-
-    set(export_name "Microsoft.GSLConfig")
-    set(namespace "Microsoft.GSL::")
-    set(cmake_files_install_dir ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
-
-    install(TARGETS GSL EXPORT ${export_name} INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
-    install(EXPORT ${export_name} NAMESPACE ${namespace} DESTINATION ${cmake_files_install_dir})
-    export(TARGETS GSL NAMESPACE ${namespace} FILE ${export_name}.cmake)
-
-    set(gls_config_version "${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake")
-
-    write_basic_package_version_file(${gls_config_version} COMPATIBILITY SameMajorVersion ARCH_INDEPENDENT)
-
-    install(FILES ${gls_config_version} DESTINATION ${cmake_files_install_dir})
-
-    install(FILES GSL.natvis DESTINATION ${cmake_files_install_dir})
-endif()
+endif ()

CONTRIBUTING.md

@@ -17,7 +17,7 @@ Please submit a Contributor License Agreement (CLA) before submitting a pull req
 Your pull request should: 
 
 * Include a description of what your change intends to do
-* Be a child commit of a reasonably recent commit in the **main** branch 
+* Be a child commit of a reasonably recent commit in the **master** branch 
     * Requests need not be a single commit, but should be a linear sequence of commits (i.e. no merge commits in your PR)
 * It is desirable, but not necessary, for the tests to pass at each commit. Please see [README.md](./README.md) for instructions to build the test suite. 
 * Have clear commit messages 

GSL.natvis

@@ -4,7 +4,13 @@
     vim: syntax=xml
 -->
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
-    <!-- These types are from the util header. -->
+    <!-- These types are from the gsl_assert header. -->
+    <Type Name="gsl::fail_fast">
+        <!-- na hides the address, otherwise it would appear as 0x.... "Message" -->
+        <DisplayString>{_Data._What,nasb}</DisplayString>
+    </Type>
+
+    <!-- These types are from the gsl_util header. -->
     <Type Name="gsl::final_action&lt;*&gt;">
         <DisplayString>{{ invoke = {invoke_}, action = {f_} }}</DisplayString>
         <Expand>
@@ -13,8 +19,7 @@
         </Expand>
     </Type>
 
-  <!-- These types are from the span header. -->
-  <Type Name="gsl::span&lt;*, *&gt;">
+    <Type Name="gsl::span&lt;*, *&gt;">
         <DisplayString>{{ extent = {storage_.size_} }}</DisplayString>
         <Expand>
             <ArrayItems>
@@ -24,7 +29,29 @@
         </Expand>
     </Type>
 
-    <!-- These types are from the pointers header. -->
+    <Type Name="gsl::basic_string_span&lt;*, *&gt;">
+        <DisplayString>{span_.storage_.data_,[span_.storage_.size_]na}</DisplayString>
+        <Expand>
+            <Item Name="[size]">span_.storage_.size_</Item>
+            <ArrayItems>
+                <Size>span_.storage_.size_</Size>
+                <ValuePointer>span_.storage_.data_</ValuePointer>
+            </ArrayItems>
+        </Expand>
+    </Type>
+
+    <Type Name="gsl::basic_zstring_span&lt;*, *&gt;">
+        <DisplayString>{span_.storage_.data_,[span_.storage_.size_]na}</DisplayString>
+        <Expand>
+            <Item Name="[size]">span_.storage_.size_</Item>
+            <ArrayItems>
+                <Size>span_.storage_.size_</Size>
+                <ValuePointer>span_.storage_.data_</ValuePointer>
+            </ArrayItems>
+        </Expand>
+    </Type>
+
+    <!-- These types are from the gsl header. -->
     <Type Name="gsl::not_null&lt;*&gt;">
         <!-- We can always dereference this since it's an invariant. -->
         <DisplayString>value = {*ptr_}</DisplayString>

README.md

@@ -1,5 +1,5 @@
 # GSL: Guidelines Support Library
-[![Build Status](https://dev.azure.com/cppstat/GSL/_apis/build/status/microsoft.GSL?branchName=main)](https://dev.azure.com/cppstat/GSL/_build/latest?definitionId=1&branchName=main)
+[![Build Status](https://dev.azure.com/cppstat/GSL/_apis/build/status/microsoft.GSL?branchName=master)](https://dev.azure.com/cppstat/GSL/_build/latest?definitionId=1&branchName=master)
 
 The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
 [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines) maintained by the [Standard C++ Foundation](https://isocpp.org).
@@ -22,59 +22,59 @@ This project makes use of the [Google Test](https://github.com/google/googletest
 # Supported features
 ## Microsoft GSL implements the following from the C++ Core Guidelines:
 
-Feature                                                                  | Supported? | Description
--------------------------------------------------------------------------|:----------:|-------------
-[**1. Views**][cg-views]                                                 |            |
-[owner](docs/headers.md#user-content-H-pointers-owner)                   | ☑   | An alias for a raw pointer
-[not_null](docs/headers.md#user-content-H-pointers-not_null)             | ☑   | Restricts a pointer/smart pointer to hold non-null values
-[span](docs/headers.md#user-content-H-span-span)                         | ☑   | A view over a contiguous sequence of memory. Based on the standardized version of `std::span`, however `gsl::span` enforces bounds checking.
-span_p                                                                   | ☐   | Spans a range starting from a pointer to the first place for which the predicate is true
-[basic_zstring](docs/headers.md#user-content-H-zstring)                  | ☑   | A pointer to a C-string (zero-terminated array) with a templated char type
-[zstring](docs/headers.md#user-content-H-zstring)                        | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `char`
-[czstring](docs/headers.md#user-content-H-zstring)                       | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `const char`
-[wzstring](docs/headers.md#user-content-H-zstring)                       | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `wchar_t`
-[cwzstring](docs/headers.md#user-content-H-zstring)                      | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `const wchar_t`
-[u16zstring](docs/headers.md#user-content-H-zstring)                     | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `char16_t`
-[cu16zstring](docs/headers.md#user-content-H-zstring)                    | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `const char16_t`
-[u32zstring](docs/headers.md#user-content-H-zstring)                     | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `char32_t`
-[cu32zstring](docs/headers.md#user-content-H-zstring)                    | ☑   | An alias to `basic_zstring` with dynamic extent and a char type of `const char32_t`
-[**2. Owners**][cg-owners]                                               |            |
-[unique_ptr](docs/headers.md#user-content-H-pointers-unique_ptr)         | ☑   | An alias to `std::unique_ptr`
-[shared_ptr](docs/headers.md#user-content-H-pointers-shared_ptr)         | ☑   | An alias to `std::shared_ptr`
-stack_array                                                              | ☐   | A stack-allocated array
-dyn_array                                                                | ☐   | A heap-allocated array
-[**3. Assertions**][cg-assertions]                                       |            |
-[Expects](docs/headers.md#user-content-H-assert-expects)                 | ☑   | A precondition assertion; on failure it terminates
-[Ensures](docs/headers.md#user-content-H-assert-ensures)                 | ☑   | A postcondition assertion; on failure it terminates
-[**4. Utilities**][cg-utilities]                                         |            |
-move_owner                                                               | ☐   | A helper function that moves one `owner` to the other
-[byte](docs/headers.md#user-content-H-byte-byte)                         | ☑   | Either an alias to `std::byte` or a byte type
-[final_action](docs/headers.md#user-content-H-util-final_action)         | ☑   | A RAII style class that invokes a functor on its destruction
-[finally](docs/headers.md#user-content-H-util-finally)                   | ☑   | A helper function instantiating [final_action](docs/headers.md#user-content-H-util-final_action)
-[GSL_SUPPRESS](docs/headers.md#user-content-H-assert-gsl_suppress)       | ☑   | A macro that takes an argument and turns it into `[[gsl::suppress(x)]]` or `[[gsl::suppress("x")]]`
-[[implicit]]                                                             | ☐   | A "marker" to put on single-argument constructors to explicitly make them non-explicit
-[index](docs/headers.md#user-content-H-util-index)                       | ☑   | A type to use for all container and array indexing (currently an alias for `std::ptrdiff_t`)
-joining_thread                                                           | ☐   | A RAII style version of `std::thread` that joins
-[narrow](docs/headers.md#user-content-H-narrow-narrow)                   | ☑   | A checked version of `narrow_cast`; it can throw [narrowing_error](docs/headers.md#user-content-H-narrow-narrowing_error)
-[narrow_cast](docs/headers.md#user-content-H-util-narrow_cast)           | ☑   | A narrowing cast for values and a synonym for `static_cast`
-[narrowing_error](docs/headers.md#user-content-H-narrow-narrowing_error) | ☑   | A custom exception type thrown by [narrow](docs/headers.md#user-content-H-narrow-narrow)
-[**5. Concepts**][cg-concepts]                                           | ☐   |
+Feature                            | Supported? | Description
+-----------------------------------|:----------:|-------------
+[**1. Views**][cg-views]           |            |
+owner                              | ☑   | an alias for a raw pointer
+not_null                           | ☑   | restricts a pointer / smart pointer to hold non-null values
+span                               | ☑   | a view over a contiguous sequence of memory. Based on the standardized verison of `std::span`, however `gsl::span` enforces bounds checking. See the [wiki](https://github.com/microsoft/GSL/wiki/gsl::span-and-std::span) for additional information.
+span_p                             | ☐   | spans a range starting from a pointer to the first place for which the predicate is true
+basic_zstring                      | ☑   | A pointer to a C-string (zero-terminated array) with a templated char type
+zstring                            | ☑   | An alias to `basic_zstring` with a char type of char
+czstring                           | ☑   | An alias to `basic_zstring` with a char type of const char
+wzstring                           | ☑   | An alias to `basic_zstring` with a char type of wchar_t
+cwzstring                          | ☑   | An alias to `basic_zstring` with a char type of const wchar_t
+u16zstring                         | ☑   | An alias to `basic_zstring` with a char type of char16_t
+cu16zstring                        | ☑   | An alias to `basic_zstring` with a char type of const char16_t
+u32zstring                         | ☑   | An alias to `basic_zstring` with a char type of char32_t
+cu32zstring                        | ☑   | An alias to `basic_zstring` with a char type of const char32_t
+[**2. Owners**][cg-owners]         |            |
+unique_ptr                         | ☑   | an alias to `std::unique_ptr`
+shared_ptr                         | ☑   | an alias to `std::shared_ptr`
+stack_array                        | ☐   | a stack-allocated array
+dyn_array                          | ☐   | a heap-allocated array
+[**3. Assertions**][cg-assertions] |            |
+Expects                            | ☑   | a precondition assertion; on failure it terminates by default if no user-installed handler
+Ensures                            | ☑   | a postcondition assertion; on failure it terminates by default if no user-installed handler
+[**4. Utilities**][cg-utilities]   |            |
+move_owner                         | ☐   | a helper function that moves one `owner` to the other
+byte                               | ☑   | either an alias to std::byte or a byte type
+final_action                       | ☑   | a RAII style class that invokes a functor on its destruction
+finally                            | ☑   | a helper function instantiating `final_action`
+GSL_SUPPRESS                       | ☑   | a macro that takes an argument and turns it into `[[gsl::suppress(x)]]` or `[[gsl::suppress("x")]]`
+[[implicit]]                       | ☐   | a "marker" to put on single-argument constructors to explicitly make them non-explicit
+index                              | ☑   | a type to use for all container and array indexing (currently an alias for std::ptrdiff_t)
+joining_thread                     | ☐   | a RAII style version of `std::thread` that joins
+narrow                             | ☑   | a checked version of narrow_cast; it can throw `narrowing_error`
+narrow_cast                        | ☑   | a narrowing cast for values and a synonym for static_cast
+narrowing_error                    | ☑   | a custom exception type thrown by `narrow()`
+[**5. Concepts**][cg-concepts]     | ☐   |
 
 ## The following features do not exist in or have been removed from the C++ Core Guidelines:
 Feature                            | Supported? | Description
 -----------------------------------|:----------:|-------------
-[strict_not_null](docs/headers.md#user-content-H-pointers-strict_not_null) | ☑   | A stricter version of [not_null](docs/headers.md#user-content-H-pointers-not_null) with explicit constructors
+strict_not_null                    | ☑   | A stricter version of `not_null` with explicit constructors
 multi_span                         | ☐   | Deprecated. Multi-dimensional span.
 strided_span                       | ☐   | Deprecated. Support for this type has been discontinued.
 basic_string_span                  | ☐   | Deprecated. Like `span` but for strings with a templated char type
-string_span                        | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `char`
-cstring_span                       | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `const char`
-wstring_span                       | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `wchar_t`
-cwstring_span                      | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `const wchar_t`
-u16string_span                     | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `char16_t`
-cu16string_span                    | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `const char16_t`
-u32string_span                     | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `char32_t`
-cu32string_span                    | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `const char32_t`
+string_span                        | ☐   | Deprecated. An alias to `basic_string_span` with a char type of char
+cstring_span                       | ☐   | Deprecated. An alias to `basic_string_span` with a char type of const char
+wstring_span                       | ☐   | Deprecated. An alias to `basic_string_span` with a char type of wchar_t
+cwstring_span                      | ☐   | Deprecated. An alias to `basic_string_span` with a char type of const wchar_t
+u16string_span                     | ☐   | Deprecated. An alias to `basic_string_span` with a char type of char16_t
+cu16string_span                    | ☐   | Deprecated. An alias to `basic_string_span` with a char type of const char16_t
+u32string_span                     | ☐   | Deprecated. An alias to `basic_string_span` with a char type of char32_t
+cu32string_span                    | ☐   | Deprecated. An alias to `basic_string_span` with a char type of const char32_t
 
 This is based on [CppCoreGuidelines semi-specification](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gsl-guidelines-support-library).
 
@@ -85,25 +85,17 @@ This is based on [CppCoreGuidelines semi-specification](https://github.com/isocp
 [cg-concepts]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslconcept-concepts
 
 # Quick Start
-## Supported Compilers / Toolsets
-The GSL officially supports the latest and previous major versions of VS with MSVC & LLVM, GCC, Clang, and XCode with Apple-Clang.
-Within these two major versions, we try to target the latest minor updates / revisions (although this may be affected by
-delays between a toolchain's release and when it becomes widely available for use).
-Below is a table showing the versions currently being tested.
+## Supported Compilers
+The GSL officially supports the current and previous major release of MSVC, GCC, Clang, and XCode's Apple-Clang.
+See our latest test results for the most up-to-date list of supported configurations.
 
 Compiler |Toolset Versions Currently Tested
 :------- |--:
- XCode | 13.2.1 & 12.5.1
- GCC | 11[^1] & 10[^2]
- Clang | 12[^2] & 11[^2]
- Visual Studio with MSVC | VS2022[^3] & VS2019[^4]
- Visual Studio with LLVM | VS2022[^3] & VS2019[^4]
-
-
-[^1]: Precise version may be found in the [latest CI results](https://dev.azure.com/cppstat/GSL/_build?definitionId=1&branchFilter=26).
-[^2]: Precise version may be found in the [latest CI results](https://dev.azure.com/cppstat/GSL/_build?definitionId=1&branchFilter=26). Should be the version specified [here](https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md#language-and-runtime).
-[^3]: Precise version may be found in the [latest CI results](https://dev.azure.com/cppstat/GSL/_build?definitionId=1&branchFilter=26). Should be the version specified [here](https://github.com/actions/virtual-environments/blob/main/images/win/Windows2022-Readme.md#visual-studio-enterprise-2022).
-[^4]: Precise version may be found in the [latest CI results](https://dev.azure.com/cppstat/GSL/_build?definitionId=1&branchFilter=26). Should be the version specified [here](https://github.com/actions/virtual-environments/blob/main/images/win/Windows2019-Readme.md#visual-studio-enterprise-2019).
+ XCode |11.4 & 10.3
+ GCC |9 & 8
+ Clang |11 &  10
+ Visual Studio with MSVC | VS2017 (15.9) & VS2019 (16.4) 
+ Visual Studio with LLVM | VS2017 (Clang 9) & VS2019 (Clang 10)
 
 ---
 If you successfully port GSL to another platform, we would love to hear from you!
@@ -121,11 +113,11 @@ Note: These CI/CD steps are run with each pull request, however failures in them
 ## Building the tests
 To build the tests, you will require the following:
 
-* [CMake](http://cmake.org), version 3.14 or later to be installed and in your PATH.
+* [CMake](http://cmake.org), version 3.1.3 (3.2.3 for AppleClang) or later to be installed and in your PATH.
 
 These steps assume the source code of this repository has been cloned into a directory named `c:\GSL`.
 
-1. Create a directory to contain the build outputs for a particular architecture (we name it `c:\GSL\build-x86` in this example).
+1. Create a directory to contain the build outputs for a particular architecture (we name it c:\GSL\build-x86 in this example).
 
         cd GSL
         md build-x86
@@ -179,40 +171,12 @@ Include the library using:
 
 ## Usage in CMake
 
-The library provides a Config file for CMake, once installed it can be found via `find_package`.
+The library provides a Config file for CMake, once installed it can be found via
+
+    find_package(Microsoft.GSL CONFIG)
 
 Which, when successful, will add library target called `Microsoft.GSL::GSL` which you can use via the usual
 `target_link_libraries` mechanism.
 
-```cmake
-find_package(Microsoft.GSL CONFIG REQUIRED)
-
-target_link_libraries(foobar PRIVATE Microsoft.GSL::GSL)
-```
-
-### FetchContent
-
-If you are using CMake version 3.11+ you can use the offical [FetchContent module](https://cmake.org/cmake/help/latest/module/FetchContent.html).
-This allows you to easily incorporate GSL into your project.
-
-```cmake
-# NOTE: This example uses CMake version 3.14 (FetchContent_MakeAvailable).
-# Since it streamlines the FetchContent process
-cmake_minimum_required(VERSION 3.14)
-
-include(FetchContent)
-
-FetchContent_Declare(GSL
-    GIT_REPOSITORY "https://github.com/microsoft/GSL"
-    GIT_TAG "v4.0.0"
-    GIT_SHALLOW ON
-)
-
-FetchContent_MakeAvailable(GSL)
-
-target_link_libraries(foobar PRIVATE Microsoft.GSL::GSL)
-```
-
 ## Debugging visualization support
-
 For Visual Studio users, the file [GSL.natvis](./GSL.natvis) in the root directory of the repository can be added to your project if you would like more helpful visualization of GSL types in the Visual Studio debugger than would be offered by default.

SECURITY.md

@@ -1,41 +0,0 @@
-<!-- BEGIN MICROSOFT SECURITY.MD V0.0.7 BLOCK -->
-
-## Security
-
-Microsoft takes the security of our software products and services seriously, which includes all source code repositories managed through our GitHub organizations, which include [Microsoft](https://github.com/Microsoft), [Azure](https://github.com/Azure), [DotNet](https://github.com/dotnet), [AspNet](https://github.com/aspnet), [Xamarin](https://github.com/xamarin), and [our GitHub organizations](https://opensource.microsoft.com/).
-
-If you believe you have found a security vulnerability in any Microsoft-owned repository that meets [Microsoft's definition of a security vulnerability](https://aka.ms/opensource/security/definition), please report it to us as described below.
-
-## Reporting Security Issues
-
-**Please do not report security vulnerabilities through public GitHub issues.**
-
-Instead, please report them to the Microsoft Security Response Center (MSRC) at [https://msrc.microsoft.com/create-report](https://aka.ms/opensource/security/create-report).
-
-If you prefer to submit without logging in, send email to [secure@microsoft.com](mailto:secure@microsoft.com).  If possible, encrypt your message with our PGP key; please download it from the [Microsoft Security Response Center PGP Key page](https://aka.ms/opensource/security/pgpkey).
-
-You should receive a response within 24 hours. If for some reason you do not, please follow up via email to ensure we received your original message. Additional information can be found at [microsoft.com/msrc](https://aka.ms/opensource/security/msrc). 
-
-Please include the requested information listed below (as much as you can provide) to help us better understand the nature and scope of the possible issue:
-
-  * Type of issue (e.g. buffer overflow, SQL injection, cross-site scripting, etc.)
-  * Full paths of source file(s) related to the manifestation of the issue
-  * The location of the affected source code (tag/branch/commit or direct URL)
-  * Any special configuration required to reproduce the issue
-  * Step-by-step instructions to reproduce the issue
-  * Proof-of-concept or exploit code (if possible)
-  * Impact of the issue, including how an attacker might exploit the issue
-
-This information will help us triage your report more quickly.
-
-If you are reporting for a bug bounty, more complete reports can contribute to a higher bounty award. Please visit our [Microsoft Bug Bounty Program](https://aka.ms/opensource/security/bounty) page for more details about our active programs.
-
-## Preferred Languages
-
-We prefer all communications to be in English.
-
-## Policy
-
-Microsoft follows the principle of [Coordinated Vulnerability Disclosure](https://aka.ms/opensource/security/cvd).
-
-<!-- END MICROSOFT SECURITY.MD BLOCK -->

appveyor.yml

@@ -0,0 +1,114 @@
+shallow_clone: true
+
+platform:
+  - x86
+  - x64
+
+configuration:
+  - Debug
+  - Release
+
+image:
+  - Visual Studio 2017
+  - Visual Studio 2019
+
+environment:
+  NINJA_TAG: v1.8.2
+  NINJA_SHA512: 9B9CE248240665FCD6404B989F3B3C27ED9682838225E6DC9B67B551774F251E4FF8A207504F941E7C811E7A8BE1945E7BCB94472A335EF15E23A0200A32E6D5
+  NINJA_PATH: C:\Tools\ninja\ninja-%NINJA_TAG%
+  VCVAR2017: 'C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat'
+  VCVAR2019: 'C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat'
+  matrix:
+    - GSL_CXX_STANDARD: 14
+      USE_TOOLSET: MSVC
+      USE_GENERATOR: MSBuild
+    - GSL_CXX_STANDARD: 17
+      USE_TOOLSET: MSVC
+      USE_GENERATOR: MSBuild
+    - GSL_CXX_STANDARD: 14
+      USE_TOOLSET: LLVM
+      USE_GENERATOR: Ninja
+    - GSL_CXX_STANDARD: 17
+      USE_TOOLSET: LLVM
+      USE_GENERATOR: Ninja
+
+cache:
+  - C:\cmake-3.14.4-win32-x86
+  - C:\Tools\ninja
+
+install:
+  - ps: |
+      if (![IO.File]::Exists("$env:NINJA_PATH\ninja.exe")) {
+        Start-FileDownload `
+          "https://github.com/ninja-build/ninja/releases/download/$env:NINJA_TAG/ninja-win.zip"
+        $hash = (Get-FileHash ninja-win.zip -Algorithm SHA512).Hash
+        if ($env:NINJA_SHA512 -eq $hash) {
+          7z e -y -bso0 ninja-win.zip -o"$env:NINJA_PATH"
+        } else { Write-Warning "Ninja download hash changed!"; Write-Output "$hash" }
+      }
+      if ([IO.File]::Exists("$env:NINJA_PATH\ninja.exe")) {
+        $env:PATH = "$env:NINJA_PATH;$env:PATH"
+      } else { Write-Warning "Failed to find ninja.exe in expected location." }
+      if ($env:USE_TOOLSET -ne "LLVM") {
+        if (![IO.File]::Exists("C:\cmake-3.14.0-win32-x86\bin\cmake.exe")) {
+          Start-FileDownload 'https://cmake.org/files/v3.14/cmake-3.14.4-win32-x86.zip'
+          7z x -y -bso0 cmake-3.14.4-win32-x86.zip -oC:\
+        }
+        $env:PATH="C:\cmake-3.14.4-win32-x86\bin;$env:PATH"
+      }
+
+before_build:
+  - ps: |
+      if ("$env:USE_GENERATOR" -eq "Ninja") {
+        $GeneratorFlags = '-k 10'
+        $Architecture = $env:PLATFORM
+        if ("$env:APPVEYOR_BUILD_WORKER_IMAGE" -eq "Visual Studio 2017") {
+          $env:VCVARSALL = "`"$env:VCVAR2017`" $Architecture"
+        } else {
+          $env:VCVARSALL = "`"$env:VCVAR2019`" $Architecture"
+        }
+        $env:CMakeGenFlags = "-G Ninja -DGSL_CXX_STANDARD=$env:GSL_CXX_STANDARD"
+      } else {
+        $GeneratorFlags = '/m /v:minimal'
+        if ("$env:APPVEYOR_BUILD_WORKER_IMAGE" -eq "Visual Studio 2017") {
+          $Generator = 'Visual Studio 15 2017'
+        } else {
+          $Generator = 'Visual Studio 16 2019'
+        }
+        if ("$env:PLATFORM" -eq "x86") {
+            $Architecture = "Win32"
+        } else {
+            $Architecture = "x64"
+        }
+        if ("$env:USE_TOOLSET" -eq "LLVM") {
+          $env:CMakeGenFlags = "-G `"$Generator`" -A $Architecture -T llvm -DGSL_CXX_STANDARD=$env:GSL_CXX_STANDARD"
+        } else {
+          $env:CMakeGenFlags = "-G `"$Generator`" -A $Architecture -DGSL_CXX_STANDARD=$env:GSL_CXX_STANDARD"
+        }
+      }
+      if ("$env:USE_TOOLSET" -eq "LLVM") {
+        $env:CC  = "clang-cl"
+        $env:CXX = "clang-cl"
+        if ("$env:PLATFORM" -eq "x86") {
+          $env:CFLAGS   = "-m32";
+          $env:CXXFLAGS = "-m32";
+        } else {
+          $env:CFLAGS   = "-m64";
+          $env:CXXFLAGS = "-m64";
+        }
+      }
+      $env:CMakeBuildFlags = "--config $env:CONFIGURATION -- $GeneratorFlags"
+  - mkdir build
+  - cd build
+  - if %USE_GENERATOR%==Ninja (call %VCVARSALL%)
+  - echo %CMakeGenFlags%
+  - cmake .. %CMakeGenFlags%
+
+build_script:
+  - echo %CMakeBuildFlags%
+  - cmake --build . %CMakeBuildFlags%
+
+test_script:
+  - ctest -j2
+
+deploy: off

azure-pipelines.yml

@@ -1,66 +1,68 @@
 trigger:
-  - main
+  - master
 
 pr:
   autoCancel: true
 
+# GCC
 stages:
 - stage: GCC
   dependsOn: []
+  variables:
+  - name: CC
+    value: gcc
+  - name: CXX
+    value: g++
   jobs:
   - template: ./pipelines/jobs.yml
     parameters:
-      compiler: gcc
-      image: ubuntu-20.04
-      compilerVersions: [ 11, 10 ]
-      setupfile: 'setup_gcc.yml'
+      jobName: 'Validate GCC latest'
+      imageName: ubuntu-20.04
+  - template: ./pipelines/jobs.yml
+    parameters:
+      jobName: 'Validate GCC Previous'
+      imageName: ubuntu-18.04
 
+# Clang
 - stage: Clang
   dependsOn: []
+  variables:
+  - name: CC
+    value: clang
+  - name: CXX
+    value: clang++
   jobs:
   - template: ./pipelines/jobs.yml
     parameters:
-      compiler: clang
-      image: ubuntu-20.04
-      compilerVersions: [ 12, 11 ]
-      setupfile: 'setup_clang.yml'
+      jobName: 'Validate Clang latest'
+      imageName: ubuntu-20.04
+  - template: ./pipelines/jobs.yml
+    parameters:
+      jobName: 'Validate Clang Previous'
+      imageName: ubuntu-18.04
 
-- stage: Xcode
+# MSVC
+- stage: MSVC
   dependsOn: []
   jobs:
   - template: ./pipelines/jobs.yml
     parameters:
-      compiler: 'Xcode'
-      image: macOS-11
-      compilerVersions: [ '12.5.1', '13.2.1' ]
-      setupfile: 'setup_apple.yml'
+      jobName: 'Validate MSVC latest'
+      imageName: windows-latest
+  - template: ./pipelines/jobs.yml
+    parameters:
+      jobName: 'Validate MSVC Previous'
+      imageName: vs2017-win2016
 
-- stage: VS_MSVC
+# Apple-Clang
+- stage: Apple_Clang
   dependsOn: []
   jobs:
   - template: ./pipelines/jobs.yml
     parameters:
-      compiler: 'VS2019 (MSVC)'
-      compilerVersions: [ 'default' ]
-      image: windows-2019
+      jobName: 'Validate Apple-Clang latest'
+      imageName: macos-10.15
   - template: ./pipelines/jobs.yml
     parameters:
-      compiler: 'VS2022 (MSVC)'
-      compilerVersions: [ 'default' ]
-      image: windows-2022
-
-- stage: VS_LLVM
-  dependsOn: []
-  jobs:
-  - template: ./pipelines/jobs.yml
-    parameters:
-      compiler: 'VS2019 (LLVM)'
-      compilerVersions: [ 'default' ]
-      image: windows-2019
-      extraCmakeArgs: '-T ClangCL'
-  - template: ./pipelines/jobs.yml
-    parameters:
-      compiler: 'VS2022 (LLVM)'
-      compilerVersions: [ 'default' ]
-      image: windows-2022
-      extraCmakeArgs: '-T ClangCL'
+      jobName: 'Validate Apple-Clang Previous'
+      imageName: macos-10.14

cmake/guidelineSupportLibrary.cmake

@@ -0,0 +1,61 @@
+# This cmake module is meant to hold helper functions/macros
+# that make maintaining the cmake build system much easier.
+# This is especially helpful since gsl needs to provide coverage
+# for multiple versions of cmake.
+#
+# Any functions/macros should have a gsl_* prefix to avoid problems
+if (DEFINED guideline_support_library_include_guard)
+    return()
+endif()
+set(guideline_support_library_include_guard ON)
+
+function(gsl_set_default_cxx_standard min_cxx_standard)
+    set(GSL_CXX_STANDARD "${min_cxx_standard}" CACHE STRING "Use c++ standard")
+
+    set(GSL_CXX_STD "cxx_std_${GSL_CXX_STANDARD}")
+
+    if (MSVC)
+        set(GSL_CXX_STD_OPT "-std:c++${GSL_CXX_STANDARD}")
+    else()
+        set(GSL_CXX_STD_OPT "-std=c++${GSL_CXX_STANDARD}")
+    endif()
+
+    # when minimum version required is 3.8.0 remove if below
+    # both branches do exactly the same thing
+    if (CMAKE_VERSION VERSION_LESS 3.7.9)
+        include(CheckCXXCompilerFlag)
+        CHECK_CXX_COMPILER_FLAG("${GSL_CXX_STD_OPT}" COMPILER_SUPPORTS_CXX_STANDARD)
+
+        if(COMPILER_SUPPORTS_CXX_STANDARD)
+            target_compile_options(GSL INTERFACE "${GSL_CXX_STD_OPT}")
+        else()
+            message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no c++${GSL_CXX_STANDARD} support. Please use a different C++ compiler.")
+        endif()
+    else()
+        target_compile_features(GSL INTERFACE "${GSL_CXX_STD}")
+        # on *nix systems force the use of -std=c++XX instead of -std=gnu++XX (default)
+        set(CMAKE_CXX_EXTENSIONS OFF)
+    endif()
+endfunction()
+
+# The best way for a project to specify the GSL's C++ standard is by the client specifying
+# the CMAKE_CXX_STANDARD. However, this isn't always ideal. Since the CMAKE_CXX_STANDARD is
+# tied to the cmake version. And many projects have low cmake minimums.
+#
+# So provide an alternative approach in case that doesn't work.
+function(gsl_client_set_cxx_standard min_cxx_standard)
+    if (DEFINED CMAKE_CXX_STANDARD)
+        if (${CMAKE_CXX_STANDARD} VERSION_LESS ${min_cxx_standard})
+            message(FATAL_ERROR "GSL: Requires at least CXX standard ${min_cxx_standard}, user provided ${CMAKE_CXX_STANDARD}")
+        endif()
+
+        # Set the GSL standard to what the client desires
+        set(GSL_CXX_STANDARD "${CMAKE_CXX_STANDARD}" PARENT_SCOPE)
+
+        # Exit out early to avoid extra unneccessary work
+        return()
+    endif()
+
+    # Otherwise pick a reasonable default
+    gsl_set_default_cxx_standard(${min_cxx_standard})
+endfunction()

docs/headers.md

@@ -1,853 +0,0 @@
-The Guidelines Support Library (GSL) interface is very lightweight and exposed via a header-only library. This document attempts to document all of the headers and their exposed classes and functions.
-
-Types and functions are exported in the namespace `gsl`.
-
-See [GSL: Guidelines support library](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#S-gsl)
-
-# <a name="H" />Headers
-
-- [`<algorithms>`](#user-content-H-algorithms)
-- [`<assert>`](#user-content-H-assert)
-- [`<byte>`](#user-content-H-byte)
-- [`<gsl>`](#user-content-H-gsl)
-- [`<narrow>`](#user-content-H-narrow)
-- [`<pointers>`](#user-content-H-pointers)
-- [`<span>`](#user-content-H-span)
-- [`<span_ext>`](#user-content-H-span_ext)
-- [`<zstring>`](#user-content-H-zstring)
-- [`<util>`](#user-content-H-util)
-
-## <a name="H-algorithms" />`<algorithms>`
-
-This header contains some common algorithms that have been wrapped in GSL safety features.
-
-- [`gsl::copy`](#user-content-H-algorithms-copy)
-
-### <a name="H-algorithms-copy" />`gsl::copy`
-
-```cpp
-template <class SrcElementType, std::size_t SrcExtent, class DestElementType,
-          std::size_t DestExtent>
-void copy(span<SrcElementType, SrcExtent> src, span<DestElementType, DestExtent> dest);
-```
-
-This function copies the content from the `src` [`span`](#user-content-H-span-span) to the `dest` [`span`](#user-content-H-span-span). It [`Expects`](#user-content-H-assert-expects)
-that the destination `span` is at least as large as the source `span`.
-
-## <a name="H-assert" />`<assert>`
-
-This header contains some macros used for contract checking and suppressing code analysis warnings.
-
-See [GSL.assert: Assertions](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-assertions)
-
-- [`GSL_SUPPRESS`](#user-content-H-assert-gsl_suppress)
-- [`Expects`](#user-content-H-assert-expects)
-- [`Ensures`](#user-content-H-assert-ensures)
-
-### <a name="H-assert-gsl_suppress" />`GSL_SUPPRESS`
-
-This macro can be used to suppress a code analysis warning.
-
-The core guidelines request tools that check for the rules to respect suppressing a rule by writing
-`[[gsl::suppress(tag)]]` or `[[gsl::suppress(tag, justification: "message")]]`.
-
-Clang does not use exactly that syntax, but requires `tag` to be put in double quotes `[[gsl::suppress("tag")]]`.
-
-For portable code you can use `GSL_SUPPRESS(tag)`.
-
-See [In.force: Enforcement](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#inforce-enforcement).
-
-### <a name="H-assert-expects" />`Expects`
-
-This macro can be used for expressing a precondition. If the precondition is not held, then `std::terminate` will be called.
-
-See [I.6: Prefer `Expects()` for expressing preconditions](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#i6-prefer-expects-for-expressing-preconditions)
-
-### <a name="H-assert-ensures" />`Ensures`
-
-This macro can be used for expressing a postcondition. If the postcondition is not held, then `std::terminate` will be called.
-
-See [I.8: Prefer `Ensures()` for expressing postconditions](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#i8-prefer-ensures-for-expressing-postconditions)
-
-## <a name="H-byte" />`<byte>`
-
-This header contains the definition of a byte type, implementing `std::byte` before it was standardized into C++17.
-
-- [`gsl::byte`](#user-content-H-byte-byte)
-
-### <a name="H-byte-byte" />`gsl::byte`
-
-If `GSL_USE_STD_BYTE` is defined to be `1`, then `gsl::byte` will be an alias to `std::byte`.  
-If `GSL_USE_STD_BYTE` is defined to be `0`, then `gsl::byte` will be a distinct type that implements the concept of byte.  
-If `GSL_USE_STD_BYTE` is not defined, then the header file will check if `std::byte` is available (C\+\+17 or higher). If yes,
-`gsl::byte` will be an alias to `std::byte`, otherwise `gsl::byte` will be a distinct type that implements the concept of byte.
-
-&#x26a0; Take care when linking projects that were compiled with different language standards (before C\+\+17 and C\+\+17 or higher).
-If you do so, you might want to `#define GSL_USE_STD_BYTE 0` to a fixed value to be sure that both projects use exactly
-the same type. Otherwise you might get linker errors.
-
-See [SL.str.5: Use `std::byte` to refer to byte values that do not necessarily represent characters](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rstr-byte)
-
-### Non-member functions
-
-```cpp
-template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
-constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept;
-
-template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
-constexpr byte operator<<(byte b, IntegerType shift) noexcept;
-
-template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
-constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept;
-
-template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
-constexpr byte operator>>(byte b, IntegerType shift) noexcept;
-```
-
-Left or right shift a `byte` by a given number of bits.
-
-```cpp
-constexpr byte& operator|=(byte& l, byte r) noexcept;
-constexpr byte operator|(byte l, byte r) noexcept;
-```
-
-Bitwise "or" of two `byte`s.
-
-```cpp
-constexpr byte& operator&=(byte& l, byte r) noexcept;
-constexpr byte operator&(byte l, byte r) noexcept;
-```
-
-Bitwise "and" of two `byte`s.
-
-```cpp
-constexpr byte& operator^=(byte& l, byte r) noexcept;
-constexpr byte operator^(byte l, byte r) noexcept;
-```
-
-Bitwise xor of two `byte`s.
-
-```cpp
-constexpr byte operator~(byte b) noexcept;
-```
-
-Bitwise negation of a `byte`. Flips all bits. Zeroes become ones, ones become zeroes.
-
-```cpp
-template <typename T>
-constexpr byte to_byte(T t) noexcept;
-```
-
-Convert the given value to a `byte`. The template requires `T` to be an `unsigned char` so that no data loss can occur.
-If you want to convert an integer constant to a `byte` you probably want to call `to_byte<integer constant>()`.
-
-```cpp
-template <int I>
-constexpr byte to_byte() noexcept;
-```
-
-Convert the given value `I` to a `byte`. The template requires `I` to be in the valid range 0..255 for a `gsl::byte`.
-
-## <a name="H-gsl" />`<gsl>`
-
-This header is a convenience header that includes all other [GSL headers](#user-content-H).
-Since `<narrow>` requires exceptions, it will only be included if exceptions are enabled.
-
-## <a name="H-narrow" />`<narrow>`
-
-This header contains utility functions and classes, for narrowing casts, which require exceptions. The narrowing-related utilities that don't require exceptions are found inside [util](#user-content-H-util).
-
-See [GSL.util: Utilities](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-utilities)
-
-- [`gsl::narrowing_error`](#user-content-H-narrow-narrowing_error)
-- [`gsl::narrow`](#user-content-H-narrow-narrow)
-
-### <a name="H-narrow-narrowing_error" />`gsl::narrowing_error`
-
-`gsl::narrowing_error` is the exception thrown by [`gsl::narrow`](#user-content-H-narrow-narrow) when a narrowing conversion fails. It is derived from `std::exception`.
-
-### <a name="H-narrow-narrow" />`gsl::narrow`
-
-`gsl::narrow<T>(x)` is a named cast that does a `static_cast<T>(x)` for narrowing conversions with no signedness promotions.
-If the argument `x` cannot be represented in the target type `T`, then the function throws a [`gsl::narrowing_error`](#user-content-H-narrow-narrowing_error) (e.g., `narrow<unsigned>(-42)` and `narrow<char>(300)` throw).
-
-Note: compare [`gsl::narrow_cast`](#user-content-H-util-narrow_cast) in header [util](#user-content-H-util).
-
-See [ES.46: Avoid lossy (narrowing, truncating) arithmetic conversions](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-narrowing) and [ES.49: If you must use a cast, use a named cast](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-casts-named)
-
-## <a name="H-pointers" />`<pointers>`
-
-This header contains some pointer types.
-
-See [GSL.view](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-views)
-
-- [`gsl::unique_ptr`](#user-content-H-pointers-unique_ptr)
-- [`gsl::shared_ptr`](#user-content-H-pointers-shared_ptr)
-- [`gsl::owner`](#user-content-H-pointers-owner)
-- [`gsl::not_null`](#user-content-H-pointers-not_null)
-- [`gsl::strict_not_null`](#user-content-H-pointers-strict_not_null)
-
-### <a name="H-pointers-unique_ptr" />`gsl::unique_ptr`
-
-`gsl::unique_ptr` is an alias to `std::unique_ptr`.
-
-See [GSL.owner: Ownership pointers](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-ownership)
-
-### <a name="H-pointers-shared_ptr" />`gsl::shared_ptr`
-
-`gsl::shared_ptr` is an alias to `std::shared_ptr`.
-
-See [GSL.owner: Ownership pointers](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-ownership)
-
-### <a name="H-pointers-owner" />`gsl::owner`
-
-`gsl::owner<T>` is designed as a safety mechanism for code that must deal directly with raw pointers that own memory. Ideally such code should be restricted to the implementation of low-level abstractions. `gsl::owner` can also be used as a stepping point in converting legacy code to use more modern RAII constructs such as smart pointers.
-`T` must be a pointer type (`std::is_pointer<T>`).
-
-A `gsl::owner<T>` is a typedef to `T`. It adds no runtime overhead whatsoever, as it is purely syntactic and does not add any runtime checks.  Instead, it serves as an annotation for static analysis tools which check for memory safety, and as a code comprehension guide for human readers.
-
-See Enforcement section of [C.31: All resources acquired by a class must be released by the class’s destructor](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-dtor-release).
-
-### <a name="H-pointers-not_null" />`gsl::not_null`
-
-`gsl::not_null<T>` restricts a pointer or smart pointer to only hold non-null values. It has no size overhead over `T`.
-
-The checks for ensuring that the pointer is not null are done in the constructor. There is no overhead when retrieving or dereferencing the checked pointer.
-When a nullptr check fails, `std::terminate` is called.
-
-See [F.23: Use a `not_null<T>` to indicate that “null” is not a valid value](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rf-nullptr)
-
-#### Member functions
-
-##### Construct/Copy
-
-```cpp
-template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
-constexpr not_null(U&& u);
-
-template <typename = std::enable_if_t<!std::is_same<std::nullptr_t, T>::value>>
-constexpr not_null(T u);
-```
-
-Constructs a `gsl_owner<T>` from a pointer that is convertible to `T` or that is a `T`. It [`Expects`](#user-content-H-assert-expects) that the provided pointer is not `== nullptr`.
-
-```cpp
-template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
-constexpr not_null(const not_null<U>& other);
-```
-
-Constructs a `gsl_owner<T>` from another `gsl_owner` where the other pointer is convertible to `T`. It [`Expects`](#user-content-H-assert-expects) that the provided pointer is not `== nullptr`.
-
-```cpp
-not_null(const not_null& other) = default;
-not_null& operator=(const not_null& other) = default;
-```
-
-Copy construction and assignment.
-
-```cpp
-not_null(std::nullptr_t) = delete;
-not_null& operator=(std::nullptr_t) = delete;
-```
-
-Construction from `std::nullptr_t`  and assignment of `std::nullptr_t` are explicitly deleted.
-
-##### Modifiers
-
-```cpp
-not_null& operator++() = delete;
-not_null& operator--() = delete;
-not_null operator++(int) = delete;
-not_null operator--(int) = delete;
-not_null& operator+=(std::ptrdiff_t) = delete;
-not_null& operator-=(std::ptrdiff_t) = delete;
-```
-
-Explicitly deleted operators. Pointers point to single objects ([I.13: Do not pass an array as a single pointer](http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Ri-array)), so don't allow these operators.
-
-##### Observers
-
-```cpp
-constexpr details::value_or_reference_return_t<T> get() const;
-constexpr operator T() const { return get(); }
-```
-
-Get the underlying pointer.
-
-```cpp
-constexpr decltype(auto) operator->() const { return get(); }
-constexpr decltype(auto) operator*() const { return *get(); }
-```
-
-Dereference the underlying pointer.
-
-```cpp
-void operator[](std::ptrdiff_t) const = delete;
-```
-
-Array index operator is explicitly deleted. Pointers point to single objects ([I.13: Do not pass an array as a single pointer](http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Ri-array)), so don't allow treating them as an array.
-
-#### Non-member functions
-
-```cpp
-template <class T>
-auto make_not_null(T&& t) noexcept;
-```
-
-Creates a `gsl::not_null` object, deducing the target type from the type of the argument.
-
-```cpp
-template <class T, class U>
-auto operator==(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(lhs.get() == rhs.get()))
-    -> decltype(lhs.get() == rhs.get());
-template <class T, class U>
-auto operator!=(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(lhs.get() != rhs.get()))
-    -> decltype(lhs.get() != rhs.get());
-template <class T, class U>
-auto operator<(const not_null<T>& lhs,
-               const not_null<U>& rhs) noexcept(noexcept(lhs.get() < rhs.get()))
-    -> decltype(lhs.get() < rhs.get());
-template <class T, class U>
-auto operator<=(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(lhs.get() <= rhs.get()))
-    -> decltype(lhs.get() <= rhs.get());
-template <class T, class U>
-auto operator>(const not_null<T>& lhs,
-               const not_null<U>& rhs) noexcept(noexcept(lhs.get() > rhs.get()))
-    -> decltype(lhs.get() > rhs.get());
-template <class T, class U>
-auto operator>=(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(lhs.get() >= rhs.get()))
-    -> decltype(lhs.get() >= rhs.get());
-```
-
-Comparison of pointers that are convertible to each other.
-
-##### Input/Output
-
-```cpp
-template <class T>
-std::ostream& operator<<(std::ostream& os, const not_null<T>& val);
-```
-
-Performs stream output on a `not_null` pointer, invoking `os << val.get()`. This function is only available when `GSL_NO_IOSTREAMS` is not defined.
-
-##### Modifiers
-
-```cpp
-template <class T, class U>
-std::ptrdiff_t operator-(const not_null<T>&, const not_null<U>&) = delete;
-template <class T>
-not_null<T> operator-(const not_null<T>&, std::ptrdiff_t) = delete;
-template <class T>
-not_null<T> operator+(const not_null<T>&, std::ptrdiff_t) = delete;
-template <class T>
-not_null<T> operator+(std::ptrdiff_t, const not_null<T>&) = delete;
-```
-
-Addition and subtraction are explicitly deleted. Pointers point to single objects ([I.13: Do not pass an array as a single pointer](http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Ri-array)), so don't allow these operators.
-
-##### STL integration
-
-```cpp
-template <class T>
-struct std::hash<gsl::not_null<T>> { ... };
-```
-
-Specialization of `std::hash` for `gsl::not_null`.
-
-### <a name="H-pointers-strict_not_null" />`gsl::strict_not_null`
-
-`strict_not_null` is the same as [`not_null`](#user-content-H-pointers-not_null) except that the constructors are `explicit`.
-
-The free function that deduces the target type from the type of the argument and creates a `gsl::strict_not_null` object is `gsl::make_strict_not_null`.
-
-## <a name="H-span" />`<span>`
-
-This header file exports the class `gsl::span`, a bounds-checked implementation of `std::span`.
-
-- [`gsl::span`](#user-content-H-span-span)
-
-### <a name="H-span-span" />`gsl::span`
-
-```cpp
-template <class ElementType, std::size_t Extent>
-class span;
-```
-
-`gsl::span` is a view over memory. It does not own the memory and is only a way to access contiguous sequences of objects.
-The extent can be either a fixed size or [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent).
-
-The `gsl::span` is based on the standardized version of `std::span` which was added to C++20. Originally, the plan was to
-deprecate `gsl::span` when `std::span` finished standardization, however that plan changed when the runtime bounds checking
-was removed from `std::span`'s design.
-
-The only difference between `gsl::span` and `std::span` is that `gsl::span` strictly enforces runtime bounds checking.
-Any violations of the bounds check results in termination of the program.
-Like `gsl::span`, `gsl::span`'s iterators also differ from `std::span`'s iterator in that all access operations are bounds checked.
-
-#### Which version of span should I use?
-
-##### Use `gsl::span` if
-
-- you want to guarantee bounds safety in your project.
-  - All data accessing operations use bounds checking to ensure you are only accessing valid memory.
-- your project uses C++14 or C++17.
-  - `std::span` is not available as it was not introduced into the STL until C++20.
-
-##### Use `std::span` if
-
-- your project is C++20 and you need the performance offered by `std::span`.
-
-#### Types
-
-```cpp
-using element_type = ElementType;
-using value_type = std::remove_cv_t<ElementType>;
-using size_type = std::size_t;
-using pointer = element_type*;
-using const_pointer = const element_type*;
-using reference = element_type&;
-using const_reference = const element_type&;
-using difference_type = std::ptrdiff_t;
-
-using iterator = details::span_iterator<ElementType>;
-using reverse_iterator = std::reverse_iterator<iterator>;
-```
-
-#### Member functions
-
-```cpp
-constexpr span() noexcept;
-```
-
-Constructs an empty `span`. This constructor is only available if `Extent` is 0 or [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent).
-`span::data()` will return `nullptr`.
-
-```cpp
-constexpr explicit(Extent != gsl::dynamic_extent) span(pointer ptr, size_type count) noexcept;
-```
-
-Constructs a `span` from a pointer and a size. If `Extent` is not [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent),
-then the constructor [`Expects`](#user-content-H-assert-expects) that `count == Extent`.
-
-```cpp
-constexpr explicit(Extent != gsl::dynamic_extent) span(pointer firstElem, pointer lastElem) noexcept;
-```
-
-Constructs a `span` from a pointer to the begin and the end of the data. If `Extent` is not [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent),
-then the constructor [`Expects`](#user-content-H-assert-expects) that `lastElem - firstElem == Extent`.
-
-```cpp
-template <std::size_t N>
-constexpr span(element_type (&arr)[N]) noexcept;
-```
-
-Constructs a `span` from a C style array. This overload is available if `Extent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)
-or `N == Extent`.
-
-```cpp
-template <class T, std::size_t N>
-constexpr span(std::array<T, N>& arr) noexcept;
-
-template <class T, std::size_t N>
-constexpr span(const std::array<T, N>& arr) noexcept;
-```
-
-Constructs a `span` from a `std::array`. These overloads are available if `Extent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)
-or `N == Extent`, and if the array can be interpreted as a `ElementType` array.
-
-```cpp
-template <class Container>
-constexpr explicit(Extent != gsl::dynamic_extent) span(Container& cont) noexcept;
-
-template <class Container>
-constexpr explicit(Extent != gsl::dynamic_extent) span(const Container& cont) noexcept;
-```
-
-Constructs a `span` from a container. These overloads are available if `Extent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)
-or `N == Extent`, and if the container can be interpreted as a contiguous `ElementType` array.
-
-```cpp
-constexpr span(const span& other) noexcept = default;
-```
-
-Copy constructor.
-
-```cpp
-template <class OtherElementType, std::size_t OtherExtent>
-explicit(Extent != gsl::dynamic_extent && OtherExtent == dynamic_extent)
-constexpr span(const span<OtherElementType, OtherExtent>& other) noexcept;
-```
-
-Constructs a `span` from another `span`. This constructor is available if `OtherExtent == Extent || Extent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)` || OtherExtent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)
-and if `ElementType` and `OtherElementType` are compatible.
-
-If `Extent !=`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent) and `OtherExtent ==`[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent),
-then the constructor [`Expects`](#user-content-H-assert-expects) that `other.size() == Extent`.
-
-```cpp
-constexpr span& operator=(const span& other) noexcept = default;
-```
-
-Copy assignment
-
-```cpp
-template <std::size_t Count>
-constexpr span<element_type, Count> first() const noexcept;
-
-constexpr span<element_type, dynamic_extent> first(size_type count) const noexcept;
-
-template <std::size_t Count>
-constexpr span<element_type, Count> last() const noexcept;
-
-constexpr span<element_type, dynamic_extent> last(size_type count) const noexcept;
-```
-
-Return a subspan of the first/last `Count` elements. [`Expects`](#user-content-H-assert-expects) that `Count` does not exceed the `span`'s size.
-
-```cpp
-template <std::size_t offset, std::size_t count = dynamic_extent>
-constexpr auto subspan() const noexcept;
-
-constexpr span<element_type, dynamic_extent>
-subspan(size_type offset, size_type count = dynamic_extent) const noexcept;
-```
-
-Return a subspan starting at `offset` and having size `count`. [`Expects`](#user-content-H-assert-expects) that `offset` does not exceed the `span`'s size,
-and that `offset == `[`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent) or `offset + count` does not exceed the `span`'s size.
-If `count` is `gsl::dynamic_extent`, the number of elements in the subspan is `size() - offset`.
-
-```cpp
-constexpr size_type size() const noexcept;
-
-constexpr size_type size_bytes() const noexcept;
-```
-
-Returns the size respective the size in bytes of the `span`.
-
-```cpp
-constexpr bool empty() const noexcept;
-```
-
-Is the `span` empty?
-
-```cpp
-constexpr reference operator[](size_type idx) const noexcept;
-```
-
-Returns a reference to the element at the given index. [`Expects`](#user-content-H-assert-expects) that `idx` is less than the `span`'s size.
-
-```cpp
-constexpr reference front() const noexcept;
-constexpr reference back() const noexcept;
-```
-
-Returns a reference to the first/last element in the `span`. [`Expects`](#user-content-H-assert-expects) that the `span` is not empty.
-
-```cpp
-constexpr pointer data() const noexcept;
-```
-
-Returns a pointer to the beginning of the contained data.
-
-```cpp
-constexpr iterator begin() const noexcept;
-constexpr iterator end() const noexcept;
-constexpr reverse_iterator rbegin() const noexcept;
-constexpr reverse_iterator rend() const noexcept;
-```
-
-Returns an iterator to the first/last normal/reverse iterator.
-
-```cpp
-template <class Type, std::size_t Extent>
-span(Type (&)[Extent]) -> span<Type, Extent>;
-
-template <class Type, std::size_t Size>
-span(std::array<Type, Size>&) -> span<Type, Size>;
-
-template <class Type, std::size_t Size>
-span(const std::array<Type, Size>&) -> span<const Type, Size>;
-
-template <class Container,
-          class Element = std::remove_pointer_t<decltype(std::declval<Container&>().data())>>
-span(Container&) -> span<Element>;
-
-template <class Container,
-          class Element = std::remove_pointer_t<decltype(std::declval<const Container&>().data())>>
-span(const Container&) -> span<Element>;
-```
-
-Deduction guides.
-
-```cpp
-template <class ElementType, std::size_t Extent>
-span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
-as_bytes(span<ElementType, Extent> s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-span<byte, details::calculate_byte_size<ElementType, Extent>::value>
-as_writable_bytes(span<ElementType, Extent> s) noexcept;
-```
-
-Converts a `span` into a `span` of `byte`s.
-
-`as_writable_bytes` will only be available for non-const `ElementType`s.
-
-## <a name="H-span_ext" />`<span_ext>`
-
-This file is a companion for and included by [`<gsl/span>`](#user-content-H-span), and should not be used on its own. It contains useful features that aren't part of the `std::span` API as found inside the STL `<span>` header (with the exception of [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent), which is included here due to implementation constraints).
-
-- [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent)
-- [`gsl::span`](#user-content-H-span_ext-span)
-- [`gsl::span` comparison operators](#user-content-H-span_ext-span_comparison_operators)
-- [`gsl::make_span`](#user-content-H-span_ext-make_span)
-- [`gsl::at`](#user-content-H-span_ext-at)
-- [`gsl::ssize`](#user-content-H-span_ext-ssize)
-- [`gsl::span` iterator functions](#user-content-H-span_ext-span_iterator_functions)
-
-### <a name="H-span_ext-dynamic_extent" />`gsl::dynamic_extent`
-
-Defines the extent value to be used by all `gsl::span` with dynamic extent. 
-
-Note: `std::dynamic_extent` is exposed by the STL `<span>` header and so ideally `gsl::dynamic_extent` would be under [`<gsl/span>`](#user-content-H-span), but to avoid cyclic dependency issues it is under `<span_ext>` instead.
-
-### <a name="H-span_ext-span" />`gsl::span`
-
-```cpp
-template <class ElementType, std::size_t Extent = dynamic_extent>
-class span;
-```
-
-Forward declaration of `gsl::span`.
-
-### <a name="H-span_ext-span_comparison_operators" />`gsl::span` comparison operators
-
-```cpp
-template <class ElementType, std::size_t FirstExtent, std::size_t SecondExtent>
-constexpr bool operator==(span<ElementType, FirstExtent> l, span<ElementType, SecondExtent> r);
-template <class ElementType, std::size_t FirstExtent, std::size_t SecondExtent>
-constexpr bool operator!=(span<ElementType, FirstExtent> l, span<ElementType, SecondExtent> r);
-template <class ElementType, std::size_t Extent>
-constexpr bool operator<(span<ElementType, Extent> l, span<ElementType, Extent> r);
-template <class ElementType, std::size_t Extent>
-constexpr bool operator<=(span<ElementType, Extent> l, span<ElementType, Extent> r);
-template <class ElementType, std::size_t Extent>
-constexpr bool operator>(span<ElementType, Extent> l, span<ElementType, Extent> r);
-template <class ElementType, std::size_t Extent>
-constexpr bool operator>=(span<ElementType, Extent> l, span<ElementType, Extent> r);
-```
-
-The comparison operators for two `span`s lexicographically compare the elements in the `span`s.
-
-### <a name="H-span_ext-make_span" />`gsl::make_span`
-
-```cpp
-template <class ElementType>
-constexpr span<ElementType> make_span(ElementType* ptr, typename span<ElementType>::size_type count);
-template <class ElementType>
-constexpr span<ElementType> make_span(ElementType* firstElem, ElementType* lastElem);
-template <class ElementType, std::size_t N>
-constexpr span<ElementType, N> make_span(ElementType (&arr)[N]) noexcept;
-template <class Container>
-constexpr span<typename Container::value_type> make_span(Container& cont);
-template <class Container>
-constexpr span<const typename Container::value_type> make_span(const Container& cont);
-template <class Ptr>
-constexpr span<typename Ptr::element_type> make_span(Ptr& cont, std::size_t count);
-template <class Ptr>
-constexpr span<typename Ptr::element_type> make_span(Ptr& cont);
-```
-
-Utility function for creating a `span` with [`gsl::dynamic_extent`](#user-content-H-span_ext-dynamic_extent) from
-- pointer and length,
-- pointer to start and pointer to end,
-- a C style array, or
-- a container.
-
-### <a name="H-span_ext-at" />`gsl::at`
-
-```cpp
-template <class ElementType, std::size_t Extent>
-constexpr ElementType& at(span<ElementType, Extent> s, index i);
-```
-
-The function `gsl::at` offers a safe way to access data with index bounds checking.
-
-This is the specialization of [`gsl::at`](#user-content-H-util-at) for [`span`](#user-content-H-span-span). It returns a reference to the `i`th element and
-[`Expects`](#user-content-H-assert-expects) that the provided index is within the bounds of the `span`.
-
-Note: `gsl::at` supports indexes up to `PTRDIFF_MAX`.
-
-### <a name="H-span_ext-ssize" />`gsl::ssize`
-
-```cpp
-template <class ElementType, std::size_t Extent>
-constexpr std::ptrdiff_t ssize(const span<ElementType, Extent>& s) noexcept;
-```
-
-Return the size of a [`span`](#user-content-H-span-span) as a `ptrdiff_t`.
-
-### <a name="H-span_ext-span_iterator_functions" />`gsl::span` iterator functions
-
-```cpp
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::iterator
-begin(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent = dynamic_extent>
-constexpr typename span<ElementType, Extent>::iterator
-end(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-rbegin(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-rend(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::iterator
-cbegin(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent = dynamic_extent>
-constexpr typename span<ElementType, Extent>::iterator
-cend(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-crbegin(const span<ElementType, Extent>& s) noexcept;
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-crend(const span<ElementType, Extent>& s) noexcept;
-```
-
-Free functions for getting a non-const/const begin/end normal/reverse iterator for a [`span`](#user-content-H-span-span).
-
-## <a name="H-zstring" />`<zstring>`
-
-This header exports a family of `*zstring` types.
-
-A `gsl::XXzstring<T>` is a typedef to `T`. It adds no checks whatsoever, it is just for having a syntax to describe
-that a pointer points to a zero terminated C style string. This helps static code analysis, and it helps human readers.
-
-`basic_zstring` is a pointer to a C-string (zero-terminated array) with a templated char type. Used to implement the rest of the `*zstring` family.  
-`zstring` is a zero terminated `char` string.  
-`czstring` is a const zero terminated `char` string.  
-`wzstring` is a zero terminated `wchar_t` string.  
-`cwzstring` is a const zero terminated `wchar_t` string.  
-`u16zstring` is a zero terminated `char16_t` string.  
-`cu16zstring` is a const zero terminated `char16_t` string.  
-`u32zstring` is a zero terminated `char32_t` string.  
-`cu32zstring` is a const zero terminated `char32_t` string.  
-
-See [GSL.view](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-views) and [SL.str.3: Use zstring or czstring to refer to a C-style, zero-terminated, sequence of characters](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rstr-zstring).
-
-## <a name="H-util" />`<util>`
-
-This header contains utility functions and classes. This header works without exceptions being available. The parts that require
-exceptions being available are in their own header file [narrow](#user-content-H-narrow).
-
-See [GSL.util: Utilities](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-utilities)
-
-- [`gsl::narrow_cast`](#user-content-H-util-narrow_cast)
-- [`gsl::final_action`](#user-content-H-util-final_action)
-- [`gsl::at`](#user-content-H-util-at)
-
-### <a name="H-util-index" />`gsl::index`
-
-An alias to `std::ptrdiff_t`. It serves as the index type for all container indexes/subscripts/sizes.
-
-### <a name="H-util-narrow_cast" />`gsl::narrow_cast`
-
-`gsl::narrow_cast<T>(x)` is a named cast that is identical to a `static_cast<T>(x)`. It exists to make clear to static code analysis tools and to human readers that a lossy conversion is acceptable.
-
-Note: compare the throwing version [`gsl::narrow`](#user-content-H-narrow-narrow) in header [narrow](#user-content-H-narrow).
-
-See [ES.46: Avoid lossy (narrowing, truncating) arithmetic conversions](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-narrowing) and [ES.49: If you must use a cast, use a named cast](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-casts-named)
-
-### <a name="H-util-final_action" />`gsl::final_action`
-
-```cpp
-template <class F>
-class final_action { ... };
-```
-
-`final_action` allows you to ensure something gets run at the end of a scope.
-
-See [E.19: Use a final_action object to express cleanup if no suitable resource handle is available](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Re-finally)
-
-#### Member functions
-
-```cpp
-explicit final_action(const F& ff) noexcept;
-explicit final_action(F&& ff) noexcept;
-```
-
-Construct an object with the action to invoke in the destructor.
-
-```cpp
-~final_action() noexcept;
-```
-
-The destructor will call the action that was passed in the constructor.
-
-```cpp
-final_action(final_action&& other) noexcept;
-final_action(const final_action&)   = delete;
-void operator=(const final_action&) = delete;
-void operator=(final_action&&)      = delete;
-```
-
-Move construction is allowed. Copy construction is deleted. Copy and move assignment are also explicitely deleted.
-
-#### <a name="H-util-finally" />Non-member functions
-```cpp
-template <class F>
-auto finally(F&& f) noexcept;
-```
-
-Creates a `gsl::final_action` object, deducing the template argument type from the type of the argument.
-
-### <a name="H-util-at" />`gsl::at`
-
-The function `gsl::at` offers a safe way to access data with index bounds checking.
-
-Note: `gsl::at` supports indexes up to `PTRDIFF_MAX`.
-
-See [ES.42: Keep use of pointers simple and straightforward](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-ptr)
-
-```cpp
-template <class T, std::size_t N>
-constexpr T& at(T (&arr)[N], const index i);
-```
-
-This overload returns a reference to the `i`s element of a C style array `arr`. It [`Expects`](#user-content-H-assert-expects) that the provided index is within the bounds of the array.
-
-```cpp
-template <class Cont>
-constexpr auto at(Cont& cont, const index i) -> decltype(cont[cont.size()]);
-```
-
-This overload returns a reference to the `i`s element of the container `cont`. It [`Expects`](#user-content-H-assert-expects) that the provided index is within the bounds of the array.
-
-```cpp
-template <class T>
-constexpr T at(const std::initializer_list<T> cont, const index i);
-```
-
-This overload returns a reference to the `i`s element of the initializer list `cont`. It [`Expects`](#user-content-H-assert-expects) that the provided index is within the bounds of the array.
-
-```cpp
-template <class T, std::size_t extent = std::dynamic_extent>
-constexpr auto at(std::span<T, extent> sp, const index i) -> decltype(sp[sp.size()]);
-```
-
-This overload returns a reference to the `i`s element of the `std::span` `sp`. It [`Expects`](#user-content-H-assert-expects) that the provided index is within the bounds of the array.
-
-For [`gsl::at`](#user-content-H-span_ext-at) for [`gsl::span`](#user-content-H-span-span) see header [`span_ext`](#user-content-H-span_ext).

include/CMakeLists.txt

@@ -1,13 +0,0 @@
-# Add include folders to the library and targets that consume it
-# the SYSTEM keyword suppresses warnings for users of the library
-#
-# By adding this directory as an include directory the user gets a
-# namespace effect.
-#
-# IE:
-#   #include <gsl/gsl>
-if(PROJECT_IS_TOP_LEVEL)
-    target_include_directories(GSL INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
-else()
-    target_include_directories(GSL SYSTEM INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
-endif()

include/gsl/algorithm

@@ -17,8 +17,8 @@
 #ifndef GSL_ALGORITHM_H
 #define GSL_ALGORITHM_H
 
-#include "assert" // for Expects
-#include "span"   // for dynamic_extent, span
+#include <gsl/assert> // for contracts
+#include <gsl/span>   // for dynamic_extent, span
 
 #include <algorithm>   // for copy_n
 #include <cstddef>     // for ptrdiff_t
@@ -27,7 +27,7 @@
 #ifdef _MSC_VER
 #pragma warning(push)
 
-// turn off some warnings that are noisy about our Expects statements
+// turn off some warnings that are noisy about our contract checks
 #pragma warning(disable : 4127) // conditional expression is constant
 #pragma warning(disable : 4996) // unsafe use of std::copy_n
 
@@ -47,7 +47,7 @@ void copy(span<SrcElementType, SrcExtent> src, span<DestElementType, DestExtent>
                       (SrcExtent <= DestExtent),
                   "Source range is longer than target range");
 
-    Expects(dest.size() >= src.size());
+    Expects(dest.size() >= src.size(), Bounds);
     // clang-format off
     GSL_SUPPRESS(stl.1) // NO-FORMAT: attribute
     // clang-format on

include/gsl/assert

@@ -14,15 +14,15 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#ifndef GSL_ASSERT_H
-#define GSL_ASSERT_H
+#ifndef GSL_CONTRACTS_H
+#define GSL_CONTRACTS_H
+
 
 //
 // Temporary until MSVC STL supports no-exceptions mode.
 // Currently terminate is a no-op in this mode, so we add termination behavior back
 //
 #if defined(_MSC_VER) && (defined(_KERNEL_MODE) || (defined(_HAS_EXCEPTIONS) && !_HAS_EXCEPTIONS))
-#define GSL_KERNEL_MODE
 
 #define GSL_MSVC_USE_STL_NOEXCEPTION_WORKAROUND
 #include <intrin.h>
@@ -46,38 +46,17 @@
 // Hopefully temporary until suppression standardization occurs
 //
 #if defined(__clang__)
-#define GSL_SUPPRESS(x) [[gsl::suppress(#x)]]
+#define GSL_SUPPRESS(x) [[gsl::suppress("x")]]
 #else
-#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && !defined(__NVCC__)
+#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
 #define GSL_SUPPRESS(x) [[gsl::suppress(x)]]
 #else
 #define GSL_SUPPRESS(x)
 #endif // _MSC_VER
 #endif // __clang__
 
-#if defined(__clang__) || defined(__GNUC__)
-#define GSL_LIKELY(x) __builtin_expect(!!(x), 1)
-#define GSL_UNLIKELY(x) __builtin_expect(!!(x), 0)
-
-#else
-
-#define GSL_LIKELY(x) (!!(x))
-#define GSL_UNLIKELY(x) (!!(x))
-#endif // defined(__clang__) || defined(__GNUC__)
-
-//
-// GSL_ASSUME(cond)
-//
-// Tell the optimizer that the predicate cond must hold. It is unspecified
-// whether or not cond is actually evaluated.
-//
-#ifdef _MSC_VER
-#define GSL_ASSUME(cond) __assume(cond)
-#elif defined(__GNUC__)
-#define GSL_ASSUME(cond) ((cond) ? static_cast<void>(0) : __builtin_unreachable())
-#else
-#define GSL_ASSUME(cond) static_cast<void>((cond) ? 0 : 0)
-#endif
+#define GSL_STRINGIFY_DETAIL(x) #x
+#define GSL_STRINGIFY(x) GSL_STRINGIFY_DETAIL(x)
 
 //
 // GSL.assert: assertions
@@ -118,16 +97,53 @@ namespace details
     }
 
 } // namespace details
+
+
+class contract_group {
+public:
+#if defined __cpp_noexcept_function_type
+    using handler = void (*)() noexcept;
+#else // VESTIGIAL, remove when no longer needed for downlevel compilers
+    using handler = void (*)();
+#endif
+    constexpr contract_group  (handler h = nullptr)  : chandler(normalize(h)) { }
+    constexpr auto set_handler(handler h) -> handler { auto old = chandler; chandler = normalize(h); return old; }
+    constexpr auto get_handler() const    -> handler { return chandler; }
+    constexpr auto expects  (bool b)      -> void    { assertion(b); }
+    constexpr auto ensures  (bool b)      -> void    { assertion(b); }
+private:
+    constexpr auto assertion(bool b)      -> void    { if (!b) chandler(); }
+    constexpr auto normalize(handler h)   -> handler { return h ? h : []()noexcept{}; }
+    handler chandler;
+};
+
+// By default, there is one violation handler per translation unit.
+// Defining GSL_GLOBAL_CONTRACT_VIOLATION_HANDLERS and compiling as
+// C++17 (or later) opts into using a global violation handler.
+#if defined GSL_GLOBAL_CONTRACT_VIOLATION_HANDLERS && __cplusplus >= 201703L
+#define GSL_CONTRACT_VIOLATION_GRANULARITY inline
+#else
+#define GSL_CONTRACT_VIOLATION_GRANULARITY static
+#endif
+
+auto GSL_CONTRACT_VIOLATION_GRANULARITY Default = contract_group( 
+#if defined GSL_UNENFORCED_ON_CONTRACT_VIOLATION
+                                      // use default == null handler
+#else // if defined GSL_TERMINATE_ON_CONTRACT_VIOLATION
+                                      &gsl::details::terminate
+#endif
+                                    );
+auto GSL_CONTRACT_VIOLATION_GRANULARITY Bounds  = Default;
+auto GSL_CONTRACT_VIOLATION_GRANULARITY Null    = Default;
+auto GSL_CONTRACT_VIOLATION_GRANULARITY Testing = Default;
+
 } // namespace gsl
 
-#define GSL_CONTRACT_CHECK(type, cond)                                                             \
-    (GSL_LIKELY(cond) ? static_cast<void>(0) : gsl::details::terminate())
-
-#define Expects(cond) GSL_CONTRACT_CHECK("Precondition", cond)
-#define Ensures(cond) GSL_CONTRACT_CHECK("Postcondition", cond)
+#define Expects(cond, kind) kind.expects(cond)
+#define Ensures(cond, kind) kind.ensures(cond)
 
 #if defined(GSL_MSVC_USE_STL_NOEXCEPTION_WORKAROUND) && defined(__clang__)
 #pragma clang diagnostic pop
 #endif
 
-#endif // GSL_ASSERT_H
+#endif // GSL_CONTRACTS_H

include/gsl/byte

@@ -17,6 +17,20 @@
 #ifndef GSL_BYTE_H
 #define GSL_BYTE_H
 
+//
+// make suppress attributes work for some compilers
+// Hopefully temporary until suppression standardization occurs
+//
+#if defined(__clang__)
+#define GSL_SUPPRESS(x) [[gsl::suppress("x")]]
+#else
+#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
+#define GSL_SUPPRESS(x) [[gsl::suppress(x)]]
+#else
+#define GSL_SUPPRESS(x)
+#endif // _MSC_VER
+#endif // __clang__
+
 #include <type_traits>
 
 // VS2017 15.8 added support for the __cpp_lib_byte definition
@@ -160,15 +174,26 @@ constexpr IntegerType to_integer(byte b) noexcept
 
 #endif // GSL_USE_STD_BYTE
 
-template <typename T>
+template <bool E, typename T>
+constexpr byte to_byte_impl(T t) noexcept
+{
+    static_assert(
+        E, "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
+           "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version.");
+    return static_cast<byte>(t);
+}
+template <>
 // NOTE: need suppression since c++14 does not allow "return {t}"
 // GSL_SUPPRESS(type.4) // NO-FORMAT: attribute // TODO: suppression does not work
+constexpr byte to_byte_impl<true, unsigned char>(unsigned char t) noexcept
+{
+    return byte(t);
+}
+
+template <typename T>
 constexpr byte to_byte(T t) noexcept
 {
-    static_assert(std::is_same<T, unsigned char>::value,
-                  "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
-                  "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version.");
-    return byte(t);
+    return to_byte_impl<std::is_same<T, unsigned char>::value, T>(t);
 }
 
 template <int I>

include/gsl/gsl

@@ -17,16 +17,17 @@
 #ifndef GSL_GSL_H
 #define GSL_GSL_H
 
-#include "algorithm"   // copy
-#include "assert"      // Ensures/Expects
-#include "byte"        // byte
-#include "pointers"    // owner, not_null
-#include "span"        // span
-#include "zstring"     // zstring
-#include "util"        // finally()/narrow_cast()...
+#include <gsl/algorithm>   // copy
+#include <gsl/assert>      // contracts
+#include <gsl/byte>        // byte
+#include <gsl/pointers>    // owner, not_null
+#include <gsl/multi_span>  // multi_span, strided_span...
+#include <gsl/span>        // span
+#include <gsl/string_span> // zstring, string_span, zstring_builder...
+#include <gsl/util>        // finally()/narrow_cast()...
 
 #ifdef __cpp_exceptions
-#include "narrow" // narrow()
+#include <gsl/narrow> // narrow()
 #endif
 
 #endif // GSL_GSL_H

include/gsl/gsl_algorithm

@@ -0,0 +1,3 @@
+#pragma once
+#pragma message("This header will soon be removed. Use <gsl/algorithm> instead of <gsl/gsl_algorithm>")
+#include <gsl/algorithm>

include/gsl/gsl_assert

@@ -0,0 +1,3 @@
+#pragma once
+#pragma message("This header will soon be removed. Use <gsl/assert> instead of <gsl/gsl_assert>")
+#include <gsl/assert>

include/gsl/gsl_byte

@@ -0,0 +1,3 @@
+#pragma once
+#pragma message("This header will soon be removed. Use <gsl/byte> instead of <gsl/gsl_byte>")
+#include <gsl/byte>

include/gsl/gsl_narrow

@@ -0,0 +1,3 @@
+#pragma once
+#pragma message("This header will soon be removed. Use <gsl/narrow> instead of <gsl/gsl_narrow>")
+#include <gsl/narrow>

include/gsl/gsl_util

@@ -0,0 +1,3 @@
+#pragma once
+#pragma message("This header will soon be removed. Use <gsl/util> instead of <gsl/gsl_util>")
+#include <gsl/util>

include/gsl/narrow

@@ -16,9 +16,8 @@
 
 #ifndef GSL_NARROW_H
 #define GSL_NARROW_H
-#include "assert"    // for GSL_SUPPRESS
-#include "util"      // for narrow_cast
-#include <exception> // for std::exception
+#include <gsl/assert> // for contracts
+#include <gsl/util>   // for narrow_cast
 namespace gsl
 {
 struct narrowing_error : public std::exception
@@ -27,53 +26,19 @@ struct narrowing_error : public std::exception
 };
 
 // narrow() : a checked version of narrow_cast() that throws if the cast changed the value
-template <class T, class U, typename std::enable_if<std::is_arithmetic<T>::value>::type* = nullptr>
+template <class T, class U>
 // clang-format off
 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
 GSL_SUPPRESS(f.6) // NO-FORMAT: attribute // TODO: MSVC /analyze does not recognise noexcept(false)
-GSL_SUPPRESS(es.46) // NO-FORMAT: attribute // The warning suggests that a floating->unsigned conversion can occur
-                                            // in the static_cast below, and that gsl::narrow should be used instead.
-                                            // Suppress this warning, since gsl::narrow is defined in terms of
-                                            // static_cast
-    // clang-format on
+// clang-format on
     constexpr T narrow(U u) noexcept(false)
 {
     constexpr const bool is_different_signedness =
         (std::is_signed<T>::value != std::is_signed<U>::value);
 
-GSL_SUPPRESS(es.103) // NO-FORMAT: attribute // don't overflow
-GSL_SUPPRESS(es.104) // NO-FORMAT: attribute // don't underflow
-GSL_SUPPRESS(p.2) // NO-FORMAT: attribute // don't rely on undefined behavior
-    const T t = narrow_cast<T>(u); // While this is technically undefined behavior in some cases (i.e., if the source value is of floating-point type
-                                   // and cannot fit into the destination integral type), the resultant behavior is benign on the platforms
-                                   // that we target (i.e., no hardware trap representations are hit).
-
-#if defined(__clang__) || defined(__GNUC__)
-    #pragma GCC diagnostic push
-    #pragma GCC diagnostic ignored "-Wfloat-equal"
-#endif
-    // Note: NaN will always throw, since NaN != NaN
-    if (static_cast<U>(t) != u || (is_different_signedness && ((t < T{}) != (u < U{}))))
-    {
-        throw narrowing_error{};
-    }
-#if defined(__clang__) || defined(__GNUC__)
-    #pragma GCC diagnostic pop
-#endif
-
-    return t;
-}
-
-template <class T, class U, typename std::enable_if<!std::is_arithmetic<T>::value>::type* = nullptr>
-// clang-format off
-GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-GSL_SUPPRESS(f.6) // NO-FORMAT: attribute // TODO: MSVC /analyze does not recognise noexcept(false)
-    // clang-format on
-    constexpr T narrow(U u) noexcept(false)
-{
     const T t = narrow_cast<T>(u);
 
-    if (static_cast<U>(t) != u)
+    if (static_cast<U>(t) != u || (is_different_signedness && ((t < T{}) != (u < U{}))))
     {
         throw narrowing_error{};
     }

include/gsl/pointers

@@ -17,14 +17,13 @@
 #ifndef GSL_POINTERS_H
 #define GSL_POINTERS_H
 
-#include "assert" // for Ensures, Expects
+#include <gsl/assert>   // for contracts
 
 #include <algorithm>    // for forward
 #include <cstddef>      // for ptrdiff_t, nullptr_t, size_t
 #include <memory>       // for shared_ptr, unique_ptr
 #include <system_error> // for hash
 #include <type_traits>  // for enable_if_t, is_convertible, is_assignable
-#include <utility>      // for declval
 
 #if !defined(GSL_NO_IOSTREAMS)
 #include <iosfwd> // for ostream
@@ -33,33 +32,6 @@
 namespace gsl
 {
 
-namespace details
-{
-    template <typename T, typename = void>
-    struct is_comparable_to_nullptr : std::false_type
-    {
-    };
-
-    template <typename T>
-    struct is_comparable_to_nullptr<
-        T,
-        std::enable_if_t<std::is_convertible<decltype(std::declval<T>() != nullptr), bool>::value>>
-        : std::true_type
-    {
-    };
-
-    // Resolves to the more efficient of `const T` or `const T&`, in the context of returning a const-qualified value
-    // of type T.
-    //
-    // Copied from cppfront's implementation of the CppCoreGuidelines F.16 (https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rf-in)
-    template<typename T>
-    using value_or_reference_return_t = std::conditional_t<
-                                            sizeof(T) < 2*sizeof(void*) && std::is_trivially_copy_constructible<T>::value,
-                                            const T,
-                                            const T&>;
-
-} // namespace details
-
 //
 // GSL.owner: ownership pointers
 //
@@ -69,9 +41,8 @@ using std::unique_ptr;
 //
 // owner
 //
-// `gsl::owner<T>` is designed as a safety mechanism for code that must deal directly with raw pointers that own memory.
-// Ideally such code should be restricted to the implementation of low-level abstractions. `gsl::owner` can also be used
-// as a stepping point in converting legacy code to use more modern RAII constructs, such as smart pointers.
+// owner<T> is designed as a bridge for code that must deal directly with owning pointers for some
+// reason
 //
 // T must be a pointer type
 // - disallow construction from any type other than pointer type
@@ -97,29 +68,30 @@ template <class T>
 class not_null
 {
 public:
-    static_assert(details::is_comparable_to_nullptr<T>::value, "T cannot be compared to nullptr.");
+    static_assert(std::is_convertible<decltype(std::declval<T>() != nullptr), bool>::value,
+                  "T cannot be compared to nullptr.");
 
     template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
-    constexpr not_null(U&& u) noexcept(std::is_nothrow_move_constructible<T>::value) : ptr_(std::forward<U>(u))
+    constexpr not_null(U&& u) : ptr_(std::forward<U>(u))
     {
-        Expects(ptr_ != nullptr);
+        Expects(ptr_ != nullptr, Null);
     }
 
     template <typename = std::enable_if_t<!std::is_same<std::nullptr_t, T>::value>>
-    constexpr not_null(T u) noexcept(std::is_nothrow_move_constructible<T>::value) : ptr_(std::move(u))
+    constexpr not_null(T u) : ptr_(std::move(u))
     {
-        Expects(ptr_ != nullptr);
+        Expects(ptr_ != nullptr, Null);
     }
 
     template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
-    constexpr not_null(const not_null<U>& other) noexcept(std::is_nothrow_move_constructible<T>::value) : not_null(other.get())
+    constexpr not_null(const not_null<U>& other) : not_null(other.get())
     {}
 
     not_null(const not_null& other) = default;
     not_null& operator=(const not_null& other) = default;
-    constexpr details::value_or_reference_return_t<T> get() const
-        noexcept(noexcept(details::value_or_reference_return_t<T>{std::declval<T&>()}))
+    constexpr std::conditional_t<std::is_copy_constructible<T>::value, T, const T&> get() const
     {
+        Ensures(ptr_ != nullptr, Null);
         return ptr_;
     }
 
@@ -177,34 +149,34 @@ auto operator!=(const not_null<T>& lhs,
 
 template <class T, class U>
 auto operator<(const not_null<T>& lhs,
-               const not_null<U>& rhs) noexcept(noexcept(std::less<>{}(lhs.get(), rhs.get())))
-    -> decltype(std::less<>{}(lhs.get(), rhs.get()))
+               const not_null<U>& rhs) noexcept(noexcept(lhs.get() < rhs.get()))
+    -> decltype(lhs.get() < rhs.get())
 {
-    return std::less<>{}(lhs.get(), rhs.get());
+    return lhs.get() < rhs.get();
 }
 
 template <class T, class U>
 auto operator<=(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(std::less_equal<>{}(lhs.get(), rhs.get())))
-    -> decltype(std::less_equal<>{}(lhs.get(), rhs.get()))
+                const not_null<U>& rhs) noexcept(noexcept(lhs.get() <= rhs.get()))
+    -> decltype(lhs.get() <= rhs.get())
 {
-    return std::less_equal<>{}(lhs.get(), rhs.get());
+    return lhs.get() <= rhs.get();
 }
 
 template <class T, class U>
 auto operator>(const not_null<T>& lhs,
-               const not_null<U>& rhs) noexcept(noexcept(std::greater<>{}(lhs.get(), rhs.get())))
-    -> decltype(std::greater<>{}(lhs.get(), rhs.get()))
+               const not_null<U>& rhs) noexcept(noexcept(lhs.get() > rhs.get()))
+    -> decltype(lhs.get() > rhs.get())
 {
-    return std::greater<>{}(lhs.get(), rhs.get());
+    return lhs.get() > rhs.get();
 }
 
 template <class T, class U>
 auto operator>=(const not_null<T>& lhs,
-                const not_null<U>& rhs) noexcept(noexcept(std::greater_equal<>{}(lhs.get(), rhs.get())))
-    -> decltype(std::greater_equal<>{}(lhs.get(), rhs.get()))
+                const not_null<U>& rhs) noexcept(noexcept(lhs.get() >= rhs.get()))
+    -> decltype(lhs.get() >= rhs.get())
 {
-    return std::greater_equal<>{}(lhs.get(), rhs.get());
+    return lhs.get() >= rhs.get();
 }
 
 // more unwanted operators
@@ -217,28 +189,14 @@ not_null<T> operator+(const not_null<T>&, std::ptrdiff_t) = delete;
 template <class T>
 not_null<T> operator+(std::ptrdiff_t, const not_null<T>&) = delete;
 
-
-template <class T, class U = decltype(std::declval<const T&>().get()), bool = std::is_default_constructible<std::hash<U>>::value>
-struct not_null_hash
-{
-    std::size_t operator()(const T& value) const { return std::hash<U>{}(value.get()); }
-};
-
-template <class T, class U>
-struct not_null_hash<T, U, false>
-{
-    not_null_hash() = delete;
-    not_null_hash(const not_null_hash&) = delete;
-    not_null_hash& operator=(const not_null_hash&) = delete;
-};
-
 } // namespace gsl
 
 namespace std
 {
 template <class T>
-struct hash<gsl::not_null<T>> : gsl::not_null_hash<gsl::not_null<T>>
+struct hash<gsl::not_null<T>>
 {
+    std::size_t operator()(const gsl::not_null<T>& value) const { return hash<T>{}(value.get()); }
 };
 
 } // namespace std
@@ -283,9 +241,7 @@ public:
     constexpr strict_not_null(const strict_not_null<U>& other) : not_null<T>(other)
     {}
 
-    // To avoid invalidating the "not null" invariant, the contained pointer is actually copied
-    // instead of moved. If it is a custom pointer, its constructor could in theory throw exceptions.
-    strict_not_null(strict_not_null&& other) noexcept(std::is_nothrow_copy_constructible<T>::value) = default;
+    strict_not_null(strict_not_null&& other) = default;
     strict_not_null(const strict_not_null& other) = default;
     strict_not_null& operator=(const strict_not_null& other) = default;
     strict_not_null& operator=(const not_null<T>& other)
@@ -339,8 +295,12 @@ strict_not_null(T) -> strict_not_null<T>;
 namespace std
 {
 template <class T>
-struct hash<gsl::strict_not_null<T>> : gsl::not_null_hash<gsl::strict_not_null<T>>
+struct hash<gsl::strict_not_null<T>>
 {
+    std::size_t operator()(const gsl::strict_not_null<T>& value) const
+    {
+        return hash<T>{}(value.get());
+    }
 };
 
 } // namespace std

include/gsl/span

@@ -17,25 +17,19 @@
 #ifndef GSL_SPAN_H
 #define GSL_SPAN_H
 
-#include "assert"   // for Expects
-#include "byte"     // for byte
-#include "span_ext" // for span specialization of gsl::at and other span-related extensions
-#include "util"     // for narrow_cast
+#include <gsl/assert> // for contracts
+#include <gsl/byte>   // for byte
+#include <gsl/util>   // for narrow_cast
 
 #include <array>       // for array
 #include <cstddef>     // for ptrdiff_t, size_t, nullptr_t
 #include <iterator>    // for reverse_iterator, distance, random_access_...
-#include <memory>      // for pointer_traits
 #include <type_traits> // for enable_if_t, declval, is_convertible, inte...
 
-#if defined(__has_include) && __has_include(<version>)
-#include <version>
-#endif
-
 #if defined(_MSC_VER) && !defined(__clang__)
 #pragma warning(push)
 
-// turn off some warnings that are noisy about our Expects statements
+// turn off some warnings that are noisy about our contract checks
 #pragma warning(disable : 4127) // conditional expression is constant
 #pragma warning(                                                                                   \
     disable : 4146) // unary minus operator applied to unsigned type, result still unsigned
@@ -63,15 +57,15 @@
 #pragma GCC diagnostic ignored "-Wsign-conversion"
 #endif
 
-// Turn off clang unsafe buffer warnings as all accessed are guarded by runtime checks
-#if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wunsafe-buffer-usage"
-#endif // defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-
 namespace gsl
 {
 
+// [views.constants], constants
+constexpr const std::size_t dynamic_extent = narrow_cast<std::size_t>(-1);
+
+template <class ElementType, std::size_t Extent = dynamic_extent>
+class span;
+
 // implementation details
 namespace details
 {
@@ -121,9 +115,6 @@ namespace details
     class span_iterator
     {
     public:
-#if defined(__cpp_lib_ranges) || (defined(_MSVC_STL_VERSION) && defined(__cpp_lib_concepts))
-        using iterator_concept = std::contiguous_iterator_tag;
-#endif // __cpp_lib_ranges
         using iterator_category = std::random_access_iterator_tag;
         using value_type = std::remove_cv_t<Type>;
         using difference_type = std::ptrdiff_t;
@@ -132,7 +123,6 @@ namespace details
 
 #ifdef _MSC_VER
         using _Unchecked_type = pointer;
-        using _Prevent_inheriting_unwrap = span_iterator;
 #endif // _MSC_VER
         constexpr span_iterator() = default;
 
@@ -147,21 +137,21 @@ namespace details
 
         constexpr reference operator*() const noexcept
         {
-            Expects(begin_ && end_);
-            Expects(begin_ <= current_ && current_ < end_);
+            Expects(begin_ && end_, Bounds);
+            Expects(begin_ <= current_ && current_ < end_, Bounds);
             return *current_;
         }
 
         constexpr pointer operator->() const noexcept
         {
-            Expects(begin_ && end_);
-            Expects(begin_ <= current_ && current_ < end_);
+            Expects(begin_ && end_, Bounds);
+            Expects(begin_ <= current_ && current_ < end_, Bounds);
             return current_;
         }
         constexpr span_iterator& operator++() noexcept
         {
-            Expects(begin_ && current_ && end_);
-            Expects(current_ < end_);
+            Expects(begin_ && current_ && end_, Bounds);
+            Expects(current_ < end_, Bounds);
             // clang-format off
             GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
             // clang-format on
@@ -178,8 +168,8 @@ namespace details
 
         constexpr span_iterator& operator--() noexcept
         {
-            Expects(begin_ && end_);
-            Expects(begin_ < current_);
+            Expects(begin_ && end_, Bounds);
+            Expects(begin_ < current_, Bounds);
             --current_;
             return *this;
         }
@@ -193,9 +183,9 @@ namespace details
 
         constexpr span_iterator& operator+=(const difference_type n) noexcept
         {
-            if (n != 0) Expects(begin_ && current_ && end_);
-            if (n > 0) Expects(end_ - current_ >= n);
-            if (n < 0) Expects(current_ - begin_ >= -n);
+            if (n != 0) Expects(begin_ && current_ && end_, Bounds);
+            if (n > 0) Expects(end_ - current_ >= n, Bounds);
+            if (n < 0) Expects(current_ - begin_ >= -n, Bounds);
             // clang-format off
             GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
             // clang-format on
@@ -218,10 +208,9 @@ namespace details
 
         constexpr span_iterator& operator-=(const difference_type n) noexcept
         {
-            if (n != 0) Expects(begin_ && current_ && end_);
-            if (n > 0) Expects(current_ - begin_ >= n);
-            if (n < 0) Expects(end_ - current_ >= -n);
-            GSL_SUPPRESS(bounds .1)
+            if (n != 0) Expects(begin_ && current_ && end_, Bounds);
+            if (n > 0) Expects(current_ - begin_ >= n, Bounds);
+            if (n < 0) Expects(end_ - current_ >= -n, Bounds);
             current_ -= n;
             return *this;
         }
@@ -238,7 +227,7 @@ namespace details
             std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
         constexpr difference_type operator-(const span_iterator<Type2>& rhs) const noexcept
         {
-            Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
+            Expects(begin_ == rhs.begin_ && end_ == rhs.end_, Bounds);
             return current_ - rhs.current_;
         }
 
@@ -252,7 +241,7 @@ namespace details
             std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
         constexpr bool operator==(const span_iterator<Type2>& rhs) const noexcept
         {
-            Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
+            Expects(begin_ == rhs.begin_ && end_ == rhs.end_, Bounds);
             return current_ == rhs.current_;
         }
 
@@ -269,7 +258,7 @@ namespace details
             std::enable_if_t<std::is_same<std::remove_cv_t<Type2>, value_type>::value, int> = 0>
         constexpr bool operator<(const span_iterator<Type2>& rhs) const noexcept
         {
-            Expects(begin_ == rhs.begin_ && end_ == rhs.end_);
+            Expects(begin_ == rhs.begin_ && end_ == rhs.end_, Bounds);
             return current_ < rhs.current_;
         }
 
@@ -305,14 +294,14 @@ namespace details
         { // test that [lhs, rhs) forms a valid range inside an STL algorithm
             Expects(lhs.begin_ == rhs.begin_ // range spans have to match
                     && lhs.end_ == rhs.end_ &&
-                    lhs.current_ <= rhs.current_); // range must not be transposed
+                    lhs.current_ <= rhs.current_, Bounds); // range must not be transposed
         }
 
         constexpr void _Verify_offset(const difference_type n) const noexcept
         { // test that *this + n is within the range of this call
-            if (n != 0) Expects(begin_ && current_ && end_);
-            if (n > 0) Expects(end_ - current_ >= n);
-            if (n < 0) Expects(current_ - begin_ >= -n);
+            if (n != 0) Expects(begin_ && current_ && end_, Bounds);
+            if (n > 0) Expects(end_ - current_ >= n, Bounds);
+            if (n < 0) Expects(current_ - begin_ >= -n, Bounds);
         }
 
         // clang-format off
@@ -345,26 +334,8 @@ namespace details
         pointer begin_ = nullptr;
         pointer end_ = nullptr;
         pointer current_ = nullptr;
-
-        template <typename Ptr>
-        friend struct std::pointer_traits;
     };
-}} // namespace gsl::details
 
-namespace std
-{
-template <class Type>
-struct pointer_traits<::gsl::details::span_iterator<Type>>
-{
-    using pointer = ::gsl::details::span_iterator<Type>;
-    using element_type = Type;
-    using difference_type = ptrdiff_t;
-
-    static constexpr element_type* to_address(const pointer i) noexcept { return i.current_; }
-};
-} // namespace std
-
-namespace gsl { namespace details {
     template <std::size_t Ext>
     class extent_type
     {
@@ -375,7 +346,7 @@ namespace gsl { namespace details {
 
         constexpr explicit extent_type(extent_type<dynamic_extent>);
 
-        constexpr explicit extent_type(size_type size) { Expects(size == Ext); }
+        constexpr explicit extent_type(size_type size) { Expects(size == Ext, Bounds); }
 
         constexpr size_type size() const noexcept { return Ext; }
 
@@ -399,7 +370,7 @@ namespace gsl { namespace details {
 
         constexpr explicit extent_type(size_type size) : size_(size)
         {
-            Expects(size != dynamic_extent);
+            Expects(size != dynamic_extent, Bounds);
         }
 
         constexpr size_type size() const noexcept { return size_; }
@@ -411,7 +382,7 @@ namespace gsl { namespace details {
     template <std::size_t Ext>
     constexpr extent_type<Ext>::extent_type(extent_type<dynamic_extent> ext)
     {
-        Expects(ext.size() == Ext);
+        Expects(ext.size() == Ext, Bounds);
     }
 
     template <class ElementType, std::size_t Extent, std::size_t Offset, std::size_t Count>
@@ -460,7 +431,7 @@ public:
     template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent != dynamic_extent, int> = 0>
     constexpr explicit span(pointer ptr, size_type count) noexcept : storage_(ptr, count)
     {
-        Expects(count == Extent);
+        Expects(count == Extent, Bounds);
     }
 
     template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
@@ -471,7 +442,7 @@ public:
     constexpr explicit span(pointer firstElem, pointer lastElem) noexcept
         : storage_(firstElem, narrow_cast<std::size_t>(lastElem - firstElem))
     {
-        Expects(lastElem - firstElem == static_cast<difference_type>(Extent));
+        Expects(lastElem - firstElem == static_cast<difference_type>(Extent), Bounds);
     }
 
     template <std::size_t MyExtent = Extent, std::enable_if_t<MyExtent == dynamic_extent, int> = 0>
@@ -582,7 +553,7 @@ public:
     template <std::size_t Count>
     constexpr span<element_type, Count> first() const noexcept
     {
-        Expects(Count <= size());
+        Expects(Count <= size(), Bounds);
         return span<element_type, Count>{data(), Count};
     }
 
@@ -592,7 +563,7 @@ public:
         // clang-format on
         constexpr span<element_type, Count> last() const noexcept
     {
-        Expects(Count <= size());
+        Expects(Count <= size(), Bounds);
         return span<element_type, Count>{data() + (size() - Count), Count};
     }
 
@@ -603,7 +574,7 @@ public:
         constexpr auto subspan() const noexcept ->
         typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type
     {
-        Expects((size() >= Offset) && (Count == dynamic_extent || (Count <= size() - Offset)));
+        Expects((size() >= Offset) && (Count == dynamic_extent || (Count <= size() - Offset)), Bounds);
         using type =
             typename details::calculate_subspan_type<ElementType, Extent, Offset, Count>::type;
         return type{data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
@@ -611,13 +582,13 @@ public:
 
     constexpr span<element_type, dynamic_extent> first(size_type count) const noexcept
     {
-        Expects(count <= size());
+        Expects(count <= size(), Bounds);
         return {data(), count};
     }
 
     constexpr span<element_type, dynamic_extent> last(size_type count) const noexcept
     {
-        Expects(count <= size());
+        Expects(count <= size(), Bounds);
         return make_subspan(size() - count, dynamic_extent, subspan_selector<Extent>{});
     }
 
@@ -630,7 +601,11 @@ public:
     // [span.obs], span observers
     constexpr size_type size() const noexcept { return storage_.size(); }
 
-    constexpr size_type size_bytes() const noexcept { return size() * sizeof(element_type); }
+    constexpr size_type size_bytes() const noexcept
+    {
+        Expects(size() < dynamic_extent / sizeof(element_type), Bounds);
+        return size() * sizeof(element_type);
+    }
 
     constexpr bool empty() const noexcept { return size() == 0; }
 
@@ -640,19 +615,19 @@ public:
     // clang-format on
     constexpr reference operator[](size_type idx) const noexcept
     {
-        Expects(idx < size());
+        Expects(idx < size(), Bounds);
         return data()[idx];
     }
 
     constexpr reference front() const noexcept
     {
-        Expects(size() > 0);
+        Expects(size() > 0, Bounds);
         return data()[0];
     }
 
     constexpr reference back() const noexcept
     {
-        Expects(size() > 0);
+        Expects(size() > 0, Bounds);
         return data()[size() - 1];
     }
 
@@ -712,12 +687,15 @@ private:
         template <class OtherExtentType>
         constexpr storage_type(KnownNotNull data, OtherExtentType ext)
             : ExtentType(ext), data_(data.p)
-        {}
+        {
+            Expects(ExtentType::size() != dynamic_extent, Bounds);
+        }
 
         template <class OtherExtentType>
         constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
         {
-            Expects(data || ExtentType::size() == 0);
+            Expects(ExtentType::size() != dynamic_extent, Bounds);
+            Expects(data || ExtentType::size() == 0, Bounds);
         }
 
         constexpr pointer data() const noexcept { return data_; }
@@ -751,11 +729,11 @@ private:
     constexpr span<element_type, dynamic_extent>
     make_subspan(size_type offset, size_type count, subspan_selector<dynamic_extent>) const noexcept
     {
-        Expects(size() >= offset);
+        Expects(size() >= offset, Bounds);
 
         if (count == dynamic_extent) { return {KnownNotNull{data() + offset}, size() - offset}; }
 
-        Expects(size() - offset >= count);
+        Expects(size() - offset >= count, Bounds);
         return {KnownNotNull{data() + offset}, count};
     }
 };
@@ -783,15 +761,8 @@ span(const Container&) -> span<Element>;
 #endif // ( defined(__cpp_deduction_guides) && (__cpp_deduction_guides >= 201611L) )
 
 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
-#if defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated" // Bug in clang-cl.exe which raises a C++17 -Wdeprecated warning about this static constexpr workaround in C++14 mode.
-#endif // defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
 template <class ElementType, std::size_t Extent>
 constexpr const typename span<ElementType, Extent>::size_type span<ElementType, Extent>::extent;
-#if defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
-#pragma clang diagnostic pop
-#endif // defined(__clang__) && defined(_MSC_VER) && defined(__cplusplus) && (__cplusplus < 201703L)
 #endif
 
 namespace details
@@ -852,8 +823,4 @@ as_writable_bytes(span<ElementType, Extent> s) noexcept
 #pragma GCC diagnostic pop
 #endif // __GNUC__ > 6
 
-#if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-#pragma clang diagnostic pop
-#endif
-
 #endif // GSL_SPAN_H

include/gsl/span_ext

@@ -27,29 +27,16 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include "assert" // GSL_KERNEL_MODE
-#include "util"   // for narrow_cast, narrow
+#include <gsl/span> // for span
+#include <gsl/util> // for narrow_cast, narrow
 
-#include <cstddef> // for ptrdiff_t, size_t
-#include <utility>
-
-#ifndef GSL_KERNEL_MODE
 #include <algorithm> // for lexicographical_compare
-#endif               // GSL_KERNEL_MODE
+#include <cstddef>   // for ptrdiff_t, size_t
+#include <utility>
 
 namespace gsl
 {
 
-// [span.views.constants], constants
-GSL_INLINE constexpr const std::size_t dynamic_extent = narrow_cast<std::size_t>(-1);
-
-template <class ElementType, std::size_t Extent = dynamic_extent>
-class span;
-
-// std::equal and std::lexicographical_compare are not /kernel compatible
-// so all comparison operators must be removed for kernel mode.
-#ifndef GSL_KERNEL_MODE
-
 // [span.comparison], span comparison operators
 template <class ElementType, std::size_t FirstExtent, std::size_t SecondExtent>
 constexpr bool operator==(span<ElementType, FirstExtent> l, span<ElementType, SecondExtent> r)
@@ -87,8 +74,6 @@ constexpr bool operator>=(span<ElementType, Extent> l, span<ElementType, Extent>
     return !(l < r);
 }
 
-#endif // GSL_KERNEL_MODE
-
 //
 // make_span() - Utility functions for creating spans
 //
@@ -123,14 +108,12 @@ constexpr span<const typename Container::value_type> make_span(const Container&
 }
 
 template <class Ptr>
-[[deprecated("This function is deprecated. See GSL issue #1092.")]]
 constexpr span<typename Ptr::element_type> make_span(Ptr& cont, std::size_t count)
 {
     return span<typename Ptr::element_type>(cont, count);
 }
 
 template <class Ptr>
-[[deprecated("This function is deprecated. See GSL issue #1092.")]]
 constexpr span<typename Ptr::element_type> make_span(Ptr& cont)
 {
     return span<typename Ptr::element_type>(cont);
@@ -141,7 +124,7 @@ template <class ElementType, std::size_t Extent>
 constexpr ElementType& at(span<ElementType, Extent> s, index i)
 {
     // No bounds checking here because it is done in span::operator[] called below
-    Ensures(i >= 0);
+    Ensures(i >= 0, Bounds);
     return s[narrow_cast<std::size_t>(i)];
 }
 

include/gsl/string_span

@@ -1,4 +1,767 @@
-#pragma once
-#pragma message(                                                                                   \
-    "This header will soon be removed. Use <gsl/zstring> instead of <gsl/string_span>")
-#include "zstring"
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef GSL_STRING_SPAN_H
+#define GSL_STRING_SPAN_H
+
+#include <gsl/assert>   // for contracts
+#include <gsl/span_ext> // for operator!=, operator==, dynamic_extent
+#include <gsl/util>     // for narrow_cast
+
+#include <algorithm> // for equal, lexicographical_compare
+#include <array>     // for array
+#include <cstddef>   // for size_t, nullptr_t
+#include <cstdint>   // for PTRDIFF_MAX
+#include <cstring>
+#include <string>      // for basic_string, allocator, char_traits
+#include <type_traits> // for declval, is_convertible, enable_if_t, add_...
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(push)
+
+// Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
+#pragma warning(disable : 26446) // TODO: bug in parser - attributes and templates
+#pragma warning(disable : 26481) // TODO: suppress does not work inside templates sometimes
+#pragma warning(disable : 4996)  // use of functions & classes marked [[deprecated]]
+#endif                           // _MSC_VER
+
+#if defined(__GNUC__) || defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#endif
+
+namespace gsl
+{
+//
+// czstring and wzstring
+//
+// These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
+// that allow static analysis to help find bugs.
+//
+// There are no additional features/semantics that we can find a way to add inside the
+// type system for these types that will not either incur significant runtime costs or
+// (sometimes needlessly) break existing programs when introduced.
+//
+
+template <typename CharT, std::size_t Extent = dynamic_extent>
+using basic_zstring = CharT*;
+
+template <std::size_t Extent = dynamic_extent>
+using czstring = basic_zstring<const char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cwzstring = basic_zstring<const wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu16zstring = basic_zstring<const char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu32zstring = basic_zstring<const char32_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using zstring = basic_zstring<char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using wzstring = basic_zstring<wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u16zstring = basic_zstring<char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u32zstring = basic_zstring<char32_t, Extent>;
+
+namespace details
+{
+    template <class CharT>
+    [[deprecated("string_span was removed from the C++ Core Guidelines. For more information, see "
+                 "isocpp/CppCoreGuidelines PR#1680")]] constexpr std::size_t
+    string_length(const CharT* str, std::size_t n)
+    {
+        if (str == nullptr || n == dynamic_extent) return 0;
+
+        const span<const CharT> str_span{str, n};
+
+        std::size_t len = 0;
+        while (len < n && str_span[len]) len++;
+
+        return len;
+    }
+} // namespace details
+
+//
+// ensure_sentinel()
+//
+// Provides a way to obtain an span from a contiguous sequence
+// that ends with a (non-inclusive) sentinel value.
+//
+// Will fail-fast if sentinel cannot be found before max elements are examined.
+//
+template <typename T, const T Sentinel>
+[[deprecated("string_span was removed from the C++ Core Guidelines. For more information, see "
+             "isocpp/CppCoreGuidelines PR#1680")]] constexpr span<T, dynamic_extent>
+ensure_sentinel(T* seq, std::size_t max = static_cast<std::size_t>(-1))
+{
+    Ensures(seq != nullptr, Null);
+
+    // clang-format off
+    GSL_SUPPRESS(f.23) // TODO: false positive // TODO: suppress does not work
+    // clang-format on
+    auto cur = seq;
+    Ensures(cur != nullptr, Null); // workaround for removing the warning
+
+    // clang-format off
+    GSL_SUPPRESS(bounds.1) // TODO: suppress does not work
+    // clang-format on
+    while (static_cast<std::size_t>(cur - seq) < max && *cur != Sentinel) ++cur;
+    Ensures(*cur == Sentinel, Bounds);
+    return {seq, static_cast<std::size_t>(cur - seq)};
+}
+
+//
+// ensure_z - creates a span for a zero terminated strings. The span will not contain the zero
+// termination. Will fail fast if a null-terminator cannot be found before the limit of size_type.
+//
+template <typename CharT>
+[[deprecated("string_span was removed from the C++ Core Guidelines. For more information, see "
+             "isocpp/CppCoreGuidelines PR#1680")]] constexpr span<CharT, dynamic_extent>
+ensure_z(CharT* const& sz, std::size_t max = static_cast<std::size_t>(-1))
+{
+    return ensure_sentinel<CharT, CharT(0)>(sz, max);
+}
+
+template <typename CharT, std::size_t N>
+constexpr span<CharT, dynamic_extent> ensure_z(CharT (&sz)[N])
+{
+    return ensure_z(&sz[0], N);
+}
+
+template <class Cont>
+[[deprecated(
+    "string_span was removed from the C++ Core Guidelines. For more information, see "
+    "isocpp/CppCoreGuidelines PR#1680")]] constexpr span<typename std::
+                                                             remove_pointer<
+                                                                 typename Cont::pointer>::type,
+                                                         dynamic_extent>
+ensure_z(Cont& cont)
+{
+    return ensure_z(cont.data(), cont.size());
+}
+
+template <typename CharT, std::size_t>
+class [[deprecated("string_span was removed from the C++ Core Guidelines. For more information, "
+                   "see isocpp/CppCoreGuidelines PR#1680")]] basic_string_span;
+
+namespace details
+{
+    template <typename T>
+    struct [[deprecated(
+        "string_span was removed from the C++ Core Guidelines. For more information, "
+        "see isocpp/CppCoreGuidelines PR#1680")]] is_basic_string_span_oracle : std::false_type{};
+
+    template <typename CharT, std::size_t Extent>
+    struct [[deprecated(
+        "string_span was removed from the C++ Core Guidelines. For more information, see "
+        "isocpp/CppCoreGuidelines PR#1680")]] is_basic_string_span_oracle<basic_string_span<CharT,
+                                                                                            Extent>>
+        : std::true_type{};
+
+    template <typename T>
+    struct [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                        "information, see isocpp/CppCoreGuidelines PR#1680")]] is_basic_string_span
+        : is_basic_string_span_oracle<std::remove_cv_t<T>>{};
+} // namespace details
+
+//
+// string_span and relatives
+//
+template <typename CharT, std::size_t Extent = dynamic_extent>
+class [[deprecated("string_span was removed from the C++ Core Guidelines. For more information, "
+                   "see isocpp/CppCoreGuidelines PR#1680")]] basic_string_span
+{
+public:
+    using element_type = CharT;
+    using value_type = std::remove_cv_t<element_type>;
+    using pointer = std::add_pointer_t<element_type>;
+    using reference = std::add_lvalue_reference_t<element_type>;
+    using const_reference = std::add_lvalue_reference_t<std::add_const_t<element_type>>;
+    using impl_type = span<element_type, Extent>;
+
+    using size_type = typename impl_type::size_type;
+    using iterator = typename impl_type::iterator;
+    using reverse_iterator = typename impl_type::reverse_iterator;
+
+    // default (empty)
+    constexpr basic_string_span() noexcept = default;
+
+    // copy
+    constexpr basic_string_span(const basic_string_span& other) noexcept = default;
+
+    // assign
+    constexpr basic_string_span& operator=(const basic_string_span& other) noexcept = default;
+
+    constexpr basic_string_span(pointer ptr, size_type length) : span_(ptr, length) {}
+    constexpr basic_string_span(pointer firstElem, pointer lastElem) : span_(firstElem, lastElem) {}
+
+    // From static arrays - if 0-terminated, remove 0 from the view
+    // All other containers allow 0s within the length, so we do not remove them
+    template <std::size_t N>
+    constexpr basic_string_span(element_type(&arr)[N]) : span_(remove_z(arr))
+    {}
+
+    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(std::array<ArrayElementType, N> & arr) noexcept : span_(arr)
+    {}
+
+    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
+    {}
+
+    // Container signature should work for basic_string after C++17 version exists
+    template <class Traits, class Allocator>
+    // GSL_SUPPRESS(bounds.4) // TODO: parser bug
+    constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator> & str)
+        : span_(&str[0], str.length())
+    {}
+
+    template <class Traits, class Allocator>
+    constexpr basic_string_span(const std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], str.length())
+    {}
+
+    // from containers. Containers must have a pointer type and data() function signatures
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(Container & cont) : span_(cont)
+    {}
+
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(const Container& cont) : span_(cont)
+    {}
+
+    // from string_span
+    template <
+        class OtherValueType, std::size_t OtherExtent,
+        class = std::enable_if_t<std::is_convertible<
+            typename basic_string_span<OtherValueType, OtherExtent>::impl_type, impl_type>::value>>
+    constexpr basic_string_span(basic_string_span<OtherValueType, OtherExtent> other)
+        : span_(other.data(), other.length())
+    {}
+
+    template <size_type Count>
+    constexpr basic_string_span<element_type, Count> first() const
+    {
+        return {span_.template first<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> first(size_type count) const
+    {
+        return {span_.first(count)};
+    }
+
+    template <size_type Count>
+    constexpr basic_string_span<element_type, Count> last() const
+    {
+        return {span_.template last<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> last(size_type count) const
+    {
+        return {span_.last(count)};
+    }
+
+    template <size_type Offset, size_type Count>
+    constexpr basic_string_span<element_type, Count> subspan() const
+    {
+        return {span_.template subspan<Offset, Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> subspan(
+        size_type offset, size_type count = dynamic_extent) const
+    {
+        return {span_.subspan(offset, count)};
+    }
+
+    constexpr reference operator[](size_type idx) const { return span_[idx]; }
+    constexpr reference operator()(size_type idx) const { return span_[idx]; }
+
+    constexpr pointer data() const { return span_.data(); }
+
+    constexpr size_type length() const noexcept { return span_.size(); }
+    constexpr size_type size() const noexcept { return span_.size(); }
+    constexpr size_type size_bytes() const noexcept { return span_.size_bytes(); }
+    constexpr size_type length_bytes() const noexcept { return span_.length_bytes(); }
+    constexpr bool empty() const noexcept { return size() == 0; }
+
+    constexpr iterator begin() const noexcept { return span_.begin(); }
+    constexpr iterator end() const noexcept { return span_.end(); }
+
+    constexpr reverse_iterator rbegin() const noexcept { return span_.rbegin(); }
+    constexpr reverse_iterator rend() const noexcept { return span_.rend(); }
+
+private:
+    static constexpr impl_type remove_z(pointer const& sz, std::size_t max)
+    {
+        return impl_type(sz, details::string_length(sz, max));
+    }
+
+    template <std::size_t N>
+    static constexpr impl_type remove_z(element_type(&sz)[N])
+    {
+        return remove_z(&sz[0], N);
+    }
+
+    impl_type span_;
+};
+
+template <std::size_t Extent = dynamic_extent>
+using string_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                               "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<const char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using wstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cwstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                 "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<const wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u16string_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                  "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu16string_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                   "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<const char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u32string_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                  "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<char32_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu32string_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                   "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_string_span<const char32_t, Extent>;
+
+//
+// to_string() allow (explicit) conversions from string_span to string
+//
+
+template <typename CharT, std::size_t Extent>
+constexpr std::basic_string<typename std::remove_const<CharT>::type>
+to_string(basic_string_span<CharT, Extent> view)
+{
+    return {view.data(), narrow_cast<std::size_t>(view.length())};
+}
+
+template <typename CharT, typename Traits = typename std::char_traits<CharT>,
+          typename Allocator = std::allocator<CharT>, typename gCharT, std::size_t Extent>
+constexpr std::basic_string<CharT, Traits, Allocator>
+to_basic_string(basic_string_span<gCharT, Extent> view)
+{
+    return {view.data(), narrow_cast<std::size_t>(view.length())};
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr basic_string_span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+    // clang-format off
+    GSL_SUPPRESS(type.1)
+    // clang-format on
+    return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
+}
+
+template <class ElementType, std::size_t Extent,
+          class = std::enable_if_t<!std::is_const<ElementType>::value>>
+constexpr basic_string_span<byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_writable_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+    // clang-format off
+    GSL_SUPPRESS(type.1)
+    // clang-format on
+    return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
+// zero-terminated string span, used to convert
+// zero-terminated spans to legacy strings
+template <typename CharT, std::size_t Extent = dynamic_extent>
+class [[deprecated("string_span was removed from the C++ Core Guidelines. For more information, "
+                   "see isocpp/CppCoreGuidelines PR#1680")]] basic_zstring_span
+{
+public:
+    using value_type = CharT;
+    using const_value_type = std::add_const_t<CharT>;
+
+    using pointer = std::add_pointer_t<value_type>;
+    using const_pointer = std::add_pointer_t<const_value_type>;
+
+    using zstring_type = basic_zstring<value_type, Extent>;
+    using const_zstring_type = basic_zstring<const_value_type, Extent>;
+
+    using impl_type = span<value_type, Extent>;
+    using string_span_type = basic_string_span<value_type, Extent>;
+
+    constexpr basic_zstring_span(impl_type s) : span_(s)
+    {
+        // expects a zero-terminated span
+        Expects(s.size() > 0, Bounds);
+        Expects(s[s.size() - 1] == value_type{}, Bounds);
+    }
+
+    // copy
+    constexpr basic_zstring_span(const basic_zstring_span& other) = default;
+
+    // move
+    constexpr basic_zstring_span(basic_zstring_span && other) = default;
+
+    // assign
+    constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
+
+    // move assign
+    constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
+
+    constexpr bool empty() const noexcept { return false; }
+
+    constexpr string_span_type as_string_span() const noexcept
+    {
+        return {span_.data(), span_.size() - 1};
+    }
+    constexpr string_span_type ensure_z() const { return gsl::ensure_z(span_); }
+
+    constexpr const_zstring_type assume_z() const noexcept { return span_.data(); }
+
+private:
+    impl_type span_;
+};
+
+template <std::size_t Max = dynamic_extent>
+using zstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<char, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using wzstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                 "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<wchar_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using u16zstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                   "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<char16_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using u32zstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                   "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<char32_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using czstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                 "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<const char, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cwzstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For more "
+                                  "information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<const wchar_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cu16zstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For "
+                                    "more information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<const char16_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cu32zstring_span [[deprecated("string_span was removed from the C++ Core Guidelines. For "
+                                    "more information, see isocpp/CppCoreGuidelines PR#1680")]] =
+    basic_zstring_span<const char32_t, Max>;
+
+// operator ==
+template <class CharT, std::size_t Extent, class T,
+          class = std::enable_if_t<
+              details::is_basic_string_span<T>::value ||
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const gsl::basic_string_span<CharT, Extent>& one, const T& other)
+{
+    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
+    return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <class CharT, std::size_t Extent, class T,
+          class = std::enable_if_t<
+              !details::is_basic_string_span<T>::value &&
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const T& one, const gsl::basic_string_span<CharT, Extent>& other)
+{
+    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
+    return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+
+// operator !=
+template <typename CharT, std::size_t Extent = dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator!=(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return !(one == other);
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(one == other);
+}
+
+// operator<
+template <typename CharT, std::size_t Extent = dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    const gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
+    return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
+    return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+#endif
+
+// operator <=
+template <typename CharT, std::size_t Extent = dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(other < one);
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(other < one);
+}
+#endif
+
+// operator>
+template <typename CharT, std::size_t Extent = dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return other < one;
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return other < one;
+}
+#endif
+
+// operator >=
+template <typename CharT, std::size_t Extent = dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
+bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename = std::enable_if_t<
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(one < other);
+}
+
+#ifndef _MSC_VER
+
+// VS treats temp and const containers as convertible to basic_string_span,
+// so the cases below are already covered by the previous operators
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other)
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::size_t Extent = dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = std::enable_if_t<
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
+bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(one < other);
+}
+#endif
+} // namespace gsl
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(pop)
+
+#endif // _MSC_VER
+
+#if defined(__GNUC__) || defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
+#endif // GSL_STRING_SPAN_H

include/gsl/util

@@ -17,22 +17,14 @@
 #ifndef GSL_UTIL_H
 #define GSL_UTIL_H
 
-#include "assert" // for Expects
+#include <gsl/assert>       // for contracts
 
 #include <array>
 #include <cstddef>          // for ptrdiff_t, size_t
-#include <limits>           // for numeric_limits
 #include <initializer_list> // for initializer_list
 #include <type_traits>      // for is_signed, integral_constant
 #include <utility>          // for exchange, forward
 
-#if defined(__has_include) && __has_include(<version>)
-#include <version>
-#if defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
-#include <span>
-#endif // __cpp_lib_span >= 202002L
-#endif //__has_include(<version>)
-
 #if defined(_MSC_VER) && !defined(__clang__)
 
 #pragma warning(push)
@@ -40,24 +32,12 @@
 
 #endif // _MSC_VER
 
-// Turn off clang unsafe buffer warnings as all accessed are guarded by runtime checks
-#if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wunsafe-buffer-usage"
-#endif // defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-
 #if defined(__cplusplus) && (__cplusplus >= 201703L)
 #define GSL_NODISCARD [[nodiscard]]
 #else
 #define GSL_NODISCARD
 #endif // defined(__cplusplus) && (__cplusplus >= 201703L)
 
-#if defined(__cpp_inline_variables)
-#define GSL_INLINE inline
-#else
-#define GSL_INLINE
-#endif
-
 namespace gsl
 {
 //
@@ -72,37 +52,48 @@ template <class F>
 class final_action
 {
 public:
-    explicit final_action(const F& ff) noexcept : f{ff} { }
-    explicit final_action(F&& ff) noexcept : f{std::move(ff)} { }
+    static_assert(!std::is_reference<F>::value && !std::is_const<F>::value &&
+                      !std::is_volatile<F>::value,
+                  "Final_action should store its callable by value");
 
-    ~final_action() noexcept { if (invoke) f(); }
+    explicit final_action(F f) noexcept : f_(std::move(f)) {}
 
     final_action(final_action&& other) noexcept
-        : f(std::move(other.f)), invoke(std::exchange(other.invoke, false))
-    { }
+        : f_(std::move(other.f_)), invoke_(std::exchange(other.invoke_, false))
+    {}
 
-    final_action(const final_action&)   = delete;
-    void operator=(const final_action&) = delete;
-    void operator=(final_action&&)      = delete;
+    final_action(const final_action&) = delete;
+    final_action& operator=(const final_action&) = delete;
+    final_action& operator=(final_action&&) = delete;
+
+    // clang-format off
+    GSL_SUPPRESS(f.6) // NO-FORMAT: attribute // terminate if throws
+    // clang-format on
+    ~final_action() noexcept
+    {
+        if (invoke_) f_();
+    }
 
 private:
-    F f;
-    bool invoke = true;
+    F f_;
+    bool invoke_{true};
 };
 
 // finally() - convenience function to generate a final_action
 template <class F>
-GSL_NODISCARD auto finally(F&& f) noexcept
+GSL_NODISCARD final_action<typename std::remove_cv<typename std::remove_reference<F>::type>::type>
+finally(F&& f) noexcept
 {
-    return final_action<std::decay_t<F>>{std::forward<F>(f)};
+    return final_action<typename std::remove_cv<typename std::remove_reference<F>::type>::type>(
+        std::forward<F>(f));
 }
 
 // narrow_cast(): a searchable way to do narrowing casts of values
 template <class T, class U>
 // clang-format off
 GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
-    constexpr T narrow_cast(U&& u) noexcept
+// clang-format on
+constexpr T narrow_cast(U&& u) noexcept
 {
     return static_cast<T>(std::forward<U>(u));
 }
@@ -114,11 +105,10 @@ template <class T, std::size_t N>
 // clang-format off
 GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
 GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
-    // clang-format on
+// clang-format on
     constexpr T& at(T (&arr)[N], const index i)
 {
-    static_assert(N <= static_cast<std::size_t>((std::numeric_limits<std::ptrdiff_t>::max)()), "We only support arrays up to PTRDIFF_MAX bytes.");
-    Expects(i >= 0 && i < narrow_cast<index>(N));
+    Expects(i >= 0 && i < narrow_cast<index>(N), Bounds);
     return arr[narrow_cast<std::size_t>(i)];
 }
 
@@ -126,10 +116,10 @@ template <class Cont>
 // clang-format off
 GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
 GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
-    // clang-format on
+// clang-format on
     constexpr auto at(Cont& cont, const index i) -> decltype(cont[cont.size()])
 {
-    Expects(i >= 0 && i < narrow_cast<index>(cont.size()));
+    Expects(i >= 0 && i < narrow_cast<index>(cont.size()), Bounds);
     using size_type = decltype(cont.size());
     return cont[narrow_cast<size_type>(i)];
 }
@@ -137,21 +127,13 @@ GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
 template <class T>
 // clang-format off
 GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
-    // clang-format on
-    constexpr T at(const std::initializer_list<T> cont, const index i)
+// clang-format on
+constexpr T at(const std::initializer_list<T> cont, const index i)
 {
-    Expects(i >= 0 && i < narrow_cast<index>(cont.size()));
+    Expects(i >= 0 && i < narrow_cast<index>(cont.size()), Bounds);
     return *(cont.begin() + i);
 }
 
-#if defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
-template <class T, std::size_t extent = std::dynamic_extent>
-constexpr auto at(std::span<T, extent> sp, const index i) -> decltype(sp[sp.size()])
-{
-    Expects(i >= 0 && i < narrow_cast<index>(sp.size()));
-    return sp[gsl::narrow_cast<std::size_t>(i)];
-}
-#endif // __cpp_lib_span >= 202002L
 } // namespace gsl
 
 #if defined(_MSC_VER) && !defined(__clang__)
@@ -160,8 +142,4 @@ constexpr auto at(std::span<T, extent> sp, const index i) -> decltype(sp[sp.size
 
 #endif // _MSC_VER
 
-#if defined(__clang__) && __has_warning("-Wunsafe-buffer-usage")
-#pragma clang diagnostic pop
-#endif
-
 #endif // GSL_UTIL_H

include/gsl/zstring

@@ -1,58 +0,0 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
-//
-// This code is licensed under the MIT License (MIT).
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE.
-//
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef GSL_ZSTRING_H
-#define GSL_ZSTRING_H
-
-#include "span_ext" // for dynamic_extent
-
-#include <cstddef>   // for size_t, nullptr_t
-
-namespace gsl
-{
-//
-// czstring and wzstring
-//
-// These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
-// that allow static analysis to help find bugs.
-//
-// There are no additional features/semantics that we can find a way to add inside the
-// type system for these types that will not either incur significant runtime costs or
-// (sometimes needlessly) break existing programs when introduced.
-//
-
-template <typename CharT, std::size_t Extent = dynamic_extent>
-using basic_zstring = CharT*;
-
-using czstring = basic_zstring<const char, dynamic_extent>;
-
-using cwzstring = basic_zstring<const wchar_t, dynamic_extent>;
-
-using cu16zstring = basic_zstring<const char16_t, dynamic_extent>;
-
-using cu32zstring = basic_zstring<const char32_t, dynamic_extent>;
-
-using zstring = basic_zstring<char, dynamic_extent>;
-
-using wzstring = basic_zstring<wchar_t, dynamic_extent>;
-
-using u16zstring = basic_zstring<char16_t, dynamic_extent>;
-
-using u32zstring = basic_zstring<char32_t, dynamic_extent>;
-
-} // namespace gsl
-
-#endif // GSL_ZSTRING_H

pipelines/jobs.yml

@@ -1,43 +1,26 @@
 parameters:
-  CXXVersions: [ 14, 17, 20 ]
-  buildTypes: [ 'Debug', 'Release' ]
-  image: ''
-
-  compiler: ''
-  compilerVersions: ["default"] # if default value, simply uses whatever version is on the machine.
-                                # the text of this default value doesn't actually matter.
-  setupfile: ''
-  extraCmakeArgs: ''
+  jobName: ''
+  imageName: ''
 
 jobs:
-- ${{ each compilerVersion in parameters.compilerVersions }}:
-  - ${{ each CXXVersion in parameters.CXXVersions }}:
-    - ${{ each buildType in parameters.buildTypes }}:
-      - job:
-        displayName: ${{ format('{0} {1} C++{2} {3}', parameters.compiler, compilerVersion, CXXVersion, buildType) }}
-        pool:
-            vmImage: ${{ parameters.image }}
-        continueOnError: false
-
-        steps:
-          - ${{ if not(eq(parameters.setupfile, '')) }}:
-            - template: ${{ parameters.setupfile }}
-              parameters:
-                version: ${{ compilerVersion }}
-
-          - task: CMake@1
-            name: Configure
-            inputs:
-              workingDirectory: build
-              cmakeArgs: '-DGSL_CXX_STANDARD=${{ CXXVersion }} -DCMAKE_BUILD_TYPE=${{ buildType }} -DCI_TESTING:BOOL=ON -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON -Werror=dev ${{ parameters.extraCmakeArgs }} .. '
-
-          - task: CMake@1
-            name: Build
-            inputs:
-              workingDirectory: build
-              cmakeArgs: '--build . '
-
-          - script: ctest . --output-on-failure --no-compress-output
-            name: CTest
-            workingDirectory: build
-            failOnStderr: true
+- job:
+  displayName: ${{ parameters.imageName }}
+  pool:
+    vmImage: ${{ parameters.imageName }}
+  strategy:
+    matrix:
+      14_debug:
+        GSL_CXX_STANDARD: '14'
+        BUILD_TYPE: 'Debug'
+      14_release:
+        GSL_CXX_STANDARD: '14'
+        BUILD_TYPE: 'Release'
+      17_debug:
+        GSL_CXX_STANDARD: '17'
+        BUILD_TYPE: 'Debug'
+      17_release:
+        GSL_CXX_STANDARD: '17'
+        BUILD_TYPE: 'Release'
+  continueOnError: false
+  steps:
+  - template: ./steps.yml

pipelines/setup_apple.yml

@@ -1,9 +0,0 @@
-parameters:
-    version: 0
-
-steps:
-  - script: |
-      if [ "${{ parameters.version }}" != "default" ]; then sudo xcode-select -switch /Applications/Xcode_${{ parameters.version }}.app; fi
-
-    displayName: "Setup Xcode Version"
-    failOnStderr: true

pipelines/setup_clang.yml

@@ -1,13 +0,0 @@
-parameters:
-    version: 0
-
-steps:
-  - script: |
-      echo "##vso[task.setvariable variable=CXX;]${CXX}"
-      echo "##vso[task.setvariable variable=CC;]${CC}"
-
-    displayName: "Setup Clang Version"
-    failOnStderr: true
-    env:
-      CC: clang-${{ parameters.version }}
-      CXX: clang++-${{ parameters.version }}

pipelines/setup_gcc.yml

@@ -1,14 +0,0 @@
-parameters:
-    version: 0
-
-steps:
-  - script: |
-      echo "##vso[task.setvariable variable=CXX;]${CXX}"
-      echo "##vso[task.setvariable variable=CC;]${CC}"
-      if [ "${{ parameters.version }}" = "11" ]; then sudo apt-get install $CXX; fi
-
-    displayName: "Setup GCC Version"
-    failOnStderr: true
-    env:
-      CC: gcc-${{ parameters.version }}
-      CXX: g++-${{ parameters.version }}

pipelines/steps.yml

@@ -0,0 +1,17 @@
+steps:
+  - task: CMake@1
+    name: Configure
+    inputs:
+      workingDirectory: build
+      cmakeArgs: '-DCMAKE_CXX_STANDARD=$(GSL_CXX_STANDARD) -DCMAKE_BUILD_TYPE=$(BUILD_TYPE) .. '
+
+  - task: CMake@1
+    name: Build
+    inputs:
+      workingDirectory: build
+      cmakeArgs: '--build . '
+
+  - script: ctest . --output-on-failure --no-compress-output
+    name: CTest
+    workingDirectory: build
+    failOnStderr: true

tests/CMakeLists.txt

@@ -1,32 +1,13 @@
-cmake_minimum_required(VERSION 3.14...3.16)
-
-project(GSLTests LANGUAGES CXX)
-
-set(GSL_CXX_STANDARD "14" CACHE STRING "Use c++ standard")
-
-set(CMAKE_CXX_STANDARD ${GSL_CXX_STANDARD})
-set(CMAKE_CXX_EXTENSIONS OFF)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
+cmake_minimum_required(VERSION 3.0.2)
 
+project(GSLTests CXX)
 include(FindPkgConfig)
-include(ExternalProject)
 
 # will make visual studio generated project group files
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
-if(CI_TESTING AND GSL_CXX_STANDARD EQUAL 20)
-    add_compile_definitions(FORCE_STD_SPAN_TESTS=1)
-endif()
-
-if(IOS)
-    add_compile_definitions(GTEST_HAS_DEATH_TEST=1 IOS_PROCESS_DELAY_WORKAROUND=1)
-endif()
-
 pkg_search_module(GTestMain gtest_main)
 if (NOT GTestMain_FOUND)
-    # No pre-installed GTest is available, try to download it using Git.
-    find_package(Git REQUIRED QUIET)
-
     configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)
     execute_process(
         COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
@@ -56,22 +37,10 @@ if (NOT GTestMain_FOUND)
     )
 endif()
 
-if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
-    find_package(Microsoft.GSL CONFIG REQUIRED)
-    enable_testing()
-
-    if (NOT DEFINED Microsoft.GSL_VERSION)
-        message(FATAL_ERROR "Microsoft.GSL_VERSION not defined!")
-    endif()
-
-    message(STATUS "Microsoft.GSL_VERSION = ${Microsoft.GSL_VERSION}")
-endif()
-
-if (MSVC AND (GSL_CXX_STANDARD GREATER_EQUAL 17))
+if (MSVC AND (GSL_CXX_STANDARD EQUAL 17))
     set(GSL_CPLUSPLUS_OPT -Zc:__cplusplus -permissive-)
 endif()
 
-include(CheckCXXCompilerFlag)
 # this interface adds compile options to how the tests are run
 # please try to keep entries ordered =)
 add_library(gsl_tests_config INTERFACE)
@@ -98,7 +67,6 @@ if(MSVC) # MSVC or simulating MSVC
         >
         $<$<CXX_COMPILER_ID:Clang>:
           -Weverything
-          -Wfloat-equal
           -Wno-c++98-compat
           -Wno-c++98-compat-pedantic
           -Wno-covered-switch-default # GTest
@@ -110,19 +78,13 @@ if(MSVC) # MSVC or simulating MSVC
           -Wno-shift-sign-overflow # GTest gtest-port.h
           -Wno-undef # GTest
           -Wno-used-but-marked-unused # GTest EXPECT_DEATH
+          -Wno-global-constructors
           $<$<EQUAL:${GSL_CXX_STANDARD},14>: # no support for [[maybe_unused]]
             -Wno-unused-member-function
             -Wno-unused-variable
-            $<$<VERSION_EQUAL:$<CXX_COMPILER_VERSION>,15.0.1>:
-              -Wno-deprecated # False positive in MSVC Clang 15.0.1 raises a C++17 warning
-            >
           >
         >
     )
-    check_cxx_compiler_flag("-Wno-reserved-identifier" WARN_RESERVED_ID)
-    if (WARN_RESERVED_ID)
-      target_compile_options(gsl_tests_config INTERFACE "-Wno-reserved-identifier")
-    endif()
 else()
     target_compile_options(gsl_tests_config INTERFACE
         -fno-strict-aliasing
@@ -135,7 +97,6 @@ else()
         -Wpedantic
         -Wshadow
         -Wsign-conversion
-        -Wfloat-equal
         -Wno-deprecated-declarations # Allow tests for [[deprecated]] elements
         $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:
           -Weverything
@@ -149,6 +110,7 @@ else()
           -Wno-unknown-attributes
           -Wno-used-but-marked-unused # GTest EXPECT_DEATH
           -Wno-weak-vtables
+          -Wno-global-constructors
           $<$<EQUAL:${GSL_CXX_STANDARD},14>: # no support for [[maybe_unused]]
             -Wno-unused-member-function
             -Wno-unused-variable
@@ -158,11 +120,6 @@ else()
           $<$<AND:$<VERSION_GREATER:$<CXX_COMPILER_VERSION>,4.99>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,6>>:
             $<$<EQUAL:${GSL_CXX_STANDARD},17>:-Wno-undefined-func-template>
           >
-          $<$<AND:$<EQUAL:${GSL_CXX_STANDARD},20>,$<OR:$<CXX_COMPILER_VERSION:11.0.0>,$<CXX_COMPILER_VERSION:10.0.0>>>:
-              -Wno-zero-as-null-pointer-constant  # failing Clang Ubuntu 20.04 tests, seems to be a bug with clang 10.0.0
-                                                  # and clang 11.0.0. (operator< is being re-written by the compiler
-                                                  # as operator<=> and raising the warning)
-          >
         >
         $<$<CXX_COMPILER_ID:AppleClang>:
           $<$<AND:$<VERSION_GREATER:$<CXX_COMPILER_VERSION>,9.1>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,10>>:
@@ -175,7 +132,8 @@ else()
           $<$<NOT:$<VERSION_LESS:$<CXX_COMPILER_VERSION>,6>>:
             -Wduplicated-cond # duplicated if-else conditions
             -Wmisleading-indentation
-            -Wnull-dereference
+            -Wno-null-dereference
+            -Wno-array-bounds
             $<$<EQUAL:${GSL_CXX_STANDARD},14>: # no support for [[maybe_unused]]
               -Wno-unused-variable
             >
@@ -186,38 +144,45 @@ else()
         >
     )
 endif(MSVC)
-check_cxx_compiler_flag("-Wno-unsafe-buffer-usage" WARN_UNSAFE_BUFFER)
-if (WARN_UNSAFE_BUFFER)
-  # This test uses very greedy heuristics such as "no pointer arithmetic on raw buffer"
-  target_compile_options(gsl_tests_config INTERFACE "-Wno-unsafe-buffer-usage")
-endif()
 
 # for tests to find the gtest header
 target_include_directories(gsl_tests_config SYSTEM INTERFACE
     googletest/googletest/include
 )
 
-add_executable(gsl_tests
-    algorithm_tests.cpp
-    assertion_tests.cpp
-    at_tests.cpp
-    byte_tests.cpp
-    notnull_tests.cpp
-    owner_tests.cpp
-    span_compatibility_tests.cpp
-    span_ext_tests.cpp
-    span_tests.cpp
-    strict_notnull_tests.cpp
-    
-    utils_tests.cpp
-)
+set_property(TARGET  PROPERTY FOLDER "GSL_tests")
+
+function(add_gsl_test name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name}
+        GSL
+        gsl_tests_config
+        ${GTestMain_LIBRARIES}
+    )
+    add_test(
+        ${name}
+        ${name}
+    )
+    # group all tests under GSL_tests
+    set_property(TARGET ${name} PROPERTY FOLDER "GSL_tests")
+endfunction()
+
+add_gsl_test(span_tests)
+add_gsl_test(span_ext_tests)
+add_gsl_test(span_compatibility_tests)
+add_gsl_test(multi_span_tests)
+add_gsl_test(strided_span_tests)
+add_gsl_test(string_span_tests)
+add_gsl_test(at_tests)
+add_gsl_test(bounds_tests)
+add_gsl_test(notnull_tests)
+add_gsl_test(assertion_tests)
+add_gsl_test(utils_tests)
+add_gsl_test(owner_tests)
+add_gsl_test(byte_tests)
+add_gsl_test(algorithm_tests)
+add_gsl_test(strict_notnull_tests)
 
-target_link_libraries(gsl_tests
-    Microsoft.GSL::GSL
-    gsl_tests_config
-    ${GTestMain_LIBRARIES}
-)
-add_test(gsl_tests gsl_tests)
 
 # No exception tests
 
@@ -246,22 +211,13 @@ if(MSVC) # MSVC or simulating MSVC
         >
         $<$<CXX_COMPILER_ID:Clang>:
           -Weverything
-          -Wfloat-equal
           -Wno-c++98-compat
           -Wno-c++98-compat-pedantic
           -Wno-missing-prototypes
           -Wno-unknown-attributes
-          $<$<EQUAL:${GSL_CXX_STANDARD},14>:
-            $<$<VERSION_EQUAL:$<CXX_COMPILER_VERSION>,15.0.1>: 
-              -Wno-deprecated # False positive in MSVC Clang 15.0.1 raises a C++17 warning
-            >
-          >
+          -Wno-global-constructors
         >
     )
-    check_cxx_compiler_flag("-Wno-reserved-identifier" WARN_RESERVED_ID)
-    if (WARN_RESERVED_ID)
-      target_compile_options(gsl_tests_config_noexcept INTERFACE "-Wno-reserved-identifier")
-    endif()
 else()
     target_compile_options(gsl_tests_config_noexcept INTERFACE
         -fno-exceptions
@@ -275,7 +231,6 @@ else()
         -Wpedantic
         -Wshadow
         -Wsign-conversion
-        -Wfloat-equal
         $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:
           -Weverything
           -Wno-c++98-compat
@@ -283,6 +238,7 @@ else()
           -Wno-missing-prototypes
           -Wno-unknown-attributes
           -Wno-weak-vtables
+          -Wno-global-constructors
         >
         $<$<CXX_COMPILER_ID:GNU>:
           -Wdouble-promotion # float implicit to double
@@ -291,7 +247,8 @@ else()
           $<$<NOT:$<VERSION_LESS:$<CXX_COMPILER_VERSION>,6>>:
             -Wduplicated-cond # duplicated if-else conditions
             -Wmisleading-indentation
-            -Wnull-dereference
+            -Wno-null-dereference
+            -Wno-array-bounds
           >
           $<$<NOT:$<VERSION_LESS:$<CXX_COMPILER_VERSION>,7>>:
             -Wduplicated-branches # identical if-else branches
@@ -302,15 +259,20 @@ else()
         >
     )
 endif(MSVC)
-check_cxx_compiler_flag("-Wno-unsafe-buffer-usage" WARN_UNSAFE_BUFFER)
-if (WARN_UNSAFE_BUFFER)
-  # This test uses very greedy heuristics such as "no pointer arithmetic on raw buffer"
-  target_compile_options(gsl_tests_config_noexcept INTERFACE "-Wno-unsafe-buffer-usage")
-endif()
 
-add_executable(gsl_noexcept_tests no_exception_ensure_tests.cpp)
-target_link_libraries(gsl_noexcept_tests
-    Microsoft.GSL::GSL
-    gsl_tests_config_noexcept
-)
-add_test(gsl_noexcept_tests gsl_noexcept_tests)
+function(add_gsl_test_noexcept name)
+    add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name}
+        GSL
+        gsl_tests_config_noexcept
+        ${GTestMain_LIBRARIES}
+    )
+    add_test(
+      ${name}
+      ${name}
+    )
+    # group all tests under GSL_tests_noexcept
+    set_property(TARGET ${name} PROPERTY FOLDER "GSL_tests_noexcept")
+endfunction()
+
+add_gsl_test_noexcept(no_exception_ensure_tests)

tests/CMakeLists.txt.in

@@ -4,7 +4,7 @@ project(googletest-download NONE)
 include(ExternalProject)
 ExternalProject_Add(googletest
   GIT_REPOSITORY    https://github.com/google/googletest.git
-  GIT_TAG           1b18723e874b256c1e39378c6774a90701d70f7a
+  GIT_TAG           703bd9caab50b139428cea1aaff9974ebee5742e
   SOURCE_DIR        "${CMAKE_CURRENT_BINARY_DIR}/googletest-src"
   BINARY_DIR        "${CMAKE_CURRENT_BINARY_DIR}/googletest-build"
   CONFIGURE_COMMAND ""

tests/algorithm_tests.cpp

@@ -14,19 +14,23 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include <array>         // for array
-#include <cstddef>       // for size_t
-#include <gsl/algorithm> // for copy
-#include <gsl/span>      // for span
 #include <gtest/gtest.h>
+#include <gsl/algorithm> // for copy
+#include <gsl/span>          // for span
+#include <array>   // for array
+#include <cstddef> // for size_t
 
-#include "deathTestCommon.h"
+namespace
+{
+    static constexpr char deathstring[] = "Expected Death";
+}
 
 namespace gsl
 {
 struct fail_fast;
 } // namespace gsl
 
+using namespace std;
 using namespace gsl;
 
 TEST(algorithm_tests, same_type)
@@ -72,8 +76,8 @@ TEST(algorithm_tests, same_type)
         std::array<int, 5> src{1, 2, 3, 4, 5};
         std::array<int, 10> dst{};
 
-        const gsl::span<int> src_span(src);
-        const gsl::span<int, 10> dst_span(dst);
+        const span<int> src_span(src);
+        const span<int, 10> dst_span(dst);
 
         copy(src_span, dst_span);
         copy(src_span, dst_span.subspan(src_span.size()));
@@ -200,11 +204,10 @@ TEST(algorithm_tests, incompatible_type)
 
 TEST(algorithm_tests, small_destination_span)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. small_destination_span";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
     std::array<int, 12> src{1, 2, 3, 4};
     std::array<int, 4> dst{};
@@ -214,9 +217,9 @@ TEST(algorithm_tests, small_destination_span)
     const span<int> dst_span_dyn(dst);
     const span<int, 4> dst_span_static(dst);
 
-    EXPECT_DEATH(copy(src_span_dyn, dst_span_dyn), expected);
-    EXPECT_DEATH(copy(src_span_dyn, dst_span_static), expected);
-    EXPECT_DEATH(copy(src_span_static, dst_span_dyn), expected);
+    EXPECT_DEATH(copy(src_span_dyn, dst_span_dyn), deathstring);
+    EXPECT_DEATH(copy(src_span_dyn, dst_span_static), deathstring);
+    EXPECT_DEATH(copy(src_span_static, dst_span_dyn), deathstring);
 
 #ifdef CONFIRM_COMPILATION_ERRORS
     copy(src_span_static, dst_span_static);

tests/assertion_tests.cpp

@@ -14,47 +14,48 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include "deathTestCommon.h"
-#include <gsl/assert> // for Ensures, Expects
 #include <gtest/gtest.h>
+#include <gsl/assert> // for fail_fast (ptr only), contracts
 
 using namespace gsl;
 
 namespace
 {
+static constexpr char deathstring[] = "Expected Death";
 
 int f(int i)
 {
-    Expects(i > 0 && i < 10);
+    Expects(i > 0 && i < 10, Testing);
     return i;
 }
 
 int g(int i)
 {
     i++;
-    Ensures(i > 0 && i < 10);
+    Ensures(i > 0 && i < 10, Testing);
     return i;
 }
 } // namespace
 
 TEST(assertion_tests, expects)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. expects";
         std::abort();
     });
 
     EXPECT_TRUE(f(2) == 2);
-    EXPECT_DEATH(f(10), GetExpectedDeathString(terminateHandler));
+    EXPECT_DEATH(f(10), deathstring);
 }
 
+
 TEST(assertion_tests, ensures)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. ensures";
         std::abort();
     });
 
     EXPECT_TRUE(g(2) == 3);
-    EXPECT_DEATH(g(9), GetExpectedDeathString(terminateHandler));
+    EXPECT_DEATH(g(9), deathstring);
 }

tests/at_tests.cpp

@@ -20,36 +20,33 @@
 
 #include <array>            // for array
 #include <cstddef>          // for size_t
-#include <exception>        // for terminate
 #include <initializer_list> // for initializer_list
 #include <vector>           // for vector
-#if defined(__cplusplus) && __cplusplus >= 202002L
-#include <span>
-#endif // __cplusplus >= 202002L
 
-#include "deathTestCommon.h"
+namespace
+{
+    static constexpr char deathstring[] = "Expected Death";
+}
 
 TEST(at_tests, static_array)
 {
     int a[4] = {1, 2, 3, 4};
     const int(&c_a)[4] = a;
 
-    for (int i = 0; i < 4; ++i)
-    {
+    for (int i = 0; i < 4; ++i) {
         EXPECT_TRUE(&gsl::at(a, i) == &a[i]);
         EXPECT_TRUE(&gsl::at(c_a, i) == &a[i]);
     }
 
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. static_array";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
-    EXPECT_DEATH(gsl::at(a, -1), expected);
-    EXPECT_DEATH(gsl::at(a, 4), expected);
-    EXPECT_DEATH(gsl::at(c_a, -1), expected);
-    EXPECT_DEATH(gsl::at(c_a, 4), expected);
+    EXPECT_DEATH(gsl::at(a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(a, 4), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, 4), deathstring);
 }
 
 TEST(at_tests, std_array)
@@ -57,22 +54,20 @@ TEST(at_tests, std_array)
     std::array<int, 4> a = {1, 2, 3, 4};
     const std::array<int, 4>& c_a = a;
 
-    for (int i = 0; i < 4; ++i)
-    {
+    for (int i = 0; i < 4; ++i) {
         EXPECT_TRUE(&gsl::at(a, i) == &a[static_cast<std::size_t>(i)]);
         EXPECT_TRUE(&gsl::at(c_a, i) == &a[static_cast<std::size_t>(i)]);
     }
 
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. std_array";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
-    EXPECT_DEATH(gsl::at(a, -1), expected);
-    EXPECT_DEATH(gsl::at(a, 4), expected);
-    EXPECT_DEATH(gsl::at(c_a, -1), expected);
-    EXPECT_DEATH(gsl::at(c_a, 4), expected);
+    EXPECT_DEATH(gsl::at(a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(a, 4), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, 4), deathstring);
 }
 
 TEST(at_tests, std_vector)
@@ -80,74 +75,42 @@ TEST(at_tests, std_vector)
     std::vector<int> a = {1, 2, 3, 4};
     const std::vector<int>& c_a = a;
 
-    for (int i = 0; i < 4; ++i)
-    {
+    for (int i = 0; i < 4; ++i) {
         EXPECT_TRUE(&gsl::at(a, i) == &a[static_cast<std::size_t>(i)]);
         EXPECT_TRUE(&gsl::at(c_a, i) == &a[static_cast<std::size_t>(i)]);
     }
 
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. std_vector";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
-    EXPECT_DEATH(gsl::at(a, -1), expected);
-    EXPECT_DEATH(gsl::at(a, 4), expected);
-    EXPECT_DEATH(gsl::at(c_a, -1), expected);
-    EXPECT_DEATH(gsl::at(c_a, 4), expected);
+    EXPECT_DEATH(gsl::at(a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(a, 4), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(c_a, 4), deathstring);
 }
 
 TEST(at_tests, InitializerList)
 {
     const std::initializer_list<int> a = {1, 2, 3, 4};
 
-    for (int i = 0; i < 4; ++i)
-    {
+    for (int i = 0; i < 4; ++i) {
         EXPECT_TRUE(gsl::at(a, i) == i + 1);
         EXPECT_TRUE(gsl::at({1, 2, 3, 4}, i) == i + 1);
     }
 
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. InitializerList";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
-    EXPECT_DEATH(gsl::at(a, -1), expected);
-    EXPECT_DEATH(gsl::at(a, 4), expected);
-    EXPECT_DEATH(gsl::at({1, 2, 3, 4}, -1), expected);
-    EXPECT_DEATH(gsl::at({1, 2, 3, 4}, 4), expected);
+    EXPECT_DEATH(gsl::at(a, -1), deathstring);
+    EXPECT_DEATH(gsl::at(a, 4), deathstring);
+    EXPECT_DEATH(gsl::at({1, 2, 3, 4}, -1), deathstring);
+    EXPECT_DEATH(gsl::at({1, 2, 3, 4}, 4), deathstring);
 }
 
-#if defined(FORCE_STD_SPAN_TESTS) || defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
-TEST(at_tests, std_span)
-{
-    std::vector<int> vec{1, 2, 3, 4, 5};
-    std::span sp{vec};
-
-    std::vector<int> cvec{1, 2, 3, 4, 5};
-    std::span csp{cvec};
-
-    for (gsl::index i = 0; i < gsl::narrow_cast<gsl::index>(vec.size()); ++i)
-    {
-        EXPECT_TRUE(&gsl::at(sp, i) == &vec[gsl::narrow_cast<size_t>(i)]);
-        EXPECT_TRUE(&gsl::at(csp, i) == &cvec[gsl::narrow_cast<size_t>(i)]);
-    }
-
-    const auto terminateHandler = std::set_terminate([] {
-        std::cerr << "Expected Death. std_span";
-        std::abort();
-    });
-    const auto expected = GetExpectedDeathString(terminateHandler);
-
-    EXPECT_DEATH(gsl::at(sp, -1), expected);
-    EXPECT_DEATH(gsl::at(sp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
-    EXPECT_DEATH(gsl::at(csp, -1), expected);
-    EXPECT_DEATH(gsl::at(csp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
-}
-#endif // defined(FORCE_STD_SPAN_TESTS) || defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
-
 #if !defined(_MSC_VER) || defined(__clang__) || _MSC_VER >= 1910
 static constexpr bool test_constexpr()
 {
@@ -156,8 +119,7 @@ static constexpr bool test_constexpr()
     std::array<int, 4> a2 = {1, 2, 3, 4};
     const std::array<int, 4>& c_a2 = a2;
 
-    for (int i = 0; i < 4; ++i)
-    {
+    for (int i = 0; i < 4; ++i) {
         if (&gsl::at(a1, i) != &a1[i]) return false;
         if (&gsl::at(c_a1, i) != &a1[i]) return false;
         // requires C++17:

tests/bounds_tests.cpp

@@ -0,0 +1,102 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <gtest/gtest.h>
+
+#include <gsl/multi_span> // for static_bounds, static_bounds_dynamic_range_t
+
+#include <cstddef> // for ptrdiff_t, size_t
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+void use(std::ptrdiff_t&) {}
+}
+
+TEST(bounds_tests, basic_bounds)
+{
+    for (auto point : static_bounds<dynamic_range, 3, 4>{2}) {
+        for (decltype(point)::size_type j = 0;
+             j < static_cast<decltype(point)::size_type>(decltype(point)::rank); j++)
+        {
+            use(j);
+            use(point[static_cast<std::size_t>(j)]);
+        }
+    }
+}
+
+TEST(bounds_tests, bounds_basic)
+{
+    static_bounds<3, 4, 5> b;
+    const auto a = b.slice();
+    (void) a;
+    static_bounds<4, dynamic_range, 2> x{4};
+    x.slice().slice();
+}
+
+TEST(bounds_tests, arrayview_iterator)
+{
+    static_bounds<4, dynamic_range, 2> bounds{3};
+
+    const auto itr = bounds.begin();
+    (void) itr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+    multi_span<int, 4, dynamic_range, 2> av(nullptr, bounds);
+
+    auto itr2 = av.cbegin();
+
+    for (auto& v : av) {
+        v = 4;
+    }
+    fill(av.begin(), av.end(), 0);
+#endif
+}
+
+TEST(bounds_tests, bounds_convertible)
+{
+    static_bounds<7, 4, 2> b1;
+    static_bounds<7, dynamic_range, 2> b2 = b1;
+    (void) b2;
+#ifdef CONFIRM_COMPILATION_ERRORS
+    static_bounds<7, dynamic_range, 1> b4 = b2;
+#endif
+
+    static_bounds<dynamic_range, dynamic_range, dynamic_range> b3 = b1;
+    static_bounds<7, 4, 2> b4 = b3;
+    (void) b4;
+
+    static_bounds<dynamic_range> b5;
+    static_bounds<34> b6;
+
+    std::set_terminate([] {
+        std::cerr << "Expected Death. bounds_convertible";
+        std::abort();
+    });
+
+    b5 = static_bounds<20>();
+    EXPECT_DEATH(b6 = b5, ".*");
+    b5 = static_bounds<34>();
+    b6 = b5;
+
+    EXPECT_TRUE(b5 == b6);
+    EXPECT_TRUE(b5.size() == b6.size());
+}
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+copy(src_span_static, dst_span_static);
+#endif

tests/byte_tests.cpp

@@ -37,6 +37,7 @@ TEST(byte_tests, construction)
         EXPECT_TRUE(static_cast<unsigned char>(b) == 4);
     }
 
+    GSL_SUPPRESS(es.49)
     {
         const byte b = byte(12);
         EXPECT_TRUE(static_cast<unsigned char>(b) == 12);
@@ -54,16 +55,10 @@ TEST(byte_tests, construction)
 
 #if defined(__cplusplus) && (__cplusplus >= 201703L)
     {
-        const byte b{14};
+        const byte b { 14 };
         EXPECT_TRUE(static_cast<unsigned char>(b) == 14);
     }
 #endif
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-    to_byte(char{});
-    to_byte(3);
-    to_byte(3u);
-#endif
 }
 
 TEST(byte_tests, bitwise_operations)
@@ -127,7 +122,7 @@ TEST(byte_tests, aliasing)
     EXPECT_TRUE(res == i);
 }
 
-} // namespace
+}
 
 #ifdef CONFIRM_COMPILATION_ERRORS
 copy(src_span_static, dst_span_static);

tests/deathTestCommon.h

@@ -1,11 +0,0 @@
-#pragma once
-#include <gsl/assert>
-
-constexpr char deathstring[] = "Expected Death";
-constexpr char failed_set_terminate_deathstring[] = ".*";
-
-// This prevents a failed call to set_terminate from failing the test suite.
-constexpr const char* GetExpectedDeathString(std::terminate_handler handle)
-{
-    return handle ? deathstring : failed_set_terminate_deathstring;
-}

tests/no_exception_ensure_tests.cpp

@@ -14,11 +14,8 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include <chrono>
 #include <cstdlib>  // for std::exit
 #include <gsl/span> // for span
-#include <iostream>
-#include <thread>
 
 int operator_subscript_no_throw() noexcept
 {
@@ -45,10 +42,6 @@ void setup_termination_handler() noexcept
 
 int main() noexcept
 {
-    std::cout << "Running main() from " __FILE__ "\n";
-#if defined(IOS_PROCESS_DELAY_WORKAROUND)
-    std::this_thread::sleep_for(std::chrono::seconds(1));
-#endif
     setup_termination_handler();
     operator_subscript_no_throw();
     return -1;

tests/notnull_tests.cpp

@@ -19,16 +19,19 @@
 #include <gsl/pointers> // for not_null, operator<, operator<=, operator>
 
 #include <algorithm> // for addressof
-#include <cstdint>   // for uint16_t
 #include <memory>    // for shared_ptr, make_shared, operator<, opera...
 #include <sstream>   // for operator<<, ostringstream, basic_ostream:...
+#include <stdint.h>  // for uint16_t
 #include <string>    // for basic_string, operator==, string, operator<<
 #include <typeinfo>  // for type_info
-#include <variant>   // for variant, monostate, get
 
-#include "deathTestCommon.h"
 using namespace gsl;
 
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
+} //namespace
+
 struct MyBase
 {
 };
@@ -53,7 +56,7 @@ template <typename T>
 struct CustomPtr
 {
     CustomPtr(T* p) : p_(p) {}
-    operator T*() const { return p_; }
+    operator T*() { return p_; }
     bool operator!=(std::nullptr_t) const { return p_ != nullptr; }
     T* p_ = nullptr;
 };
@@ -61,9 +64,7 @@ struct CustomPtr
 template <typename T, typename U>
 std::string operator==(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) == reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -71,9 +72,7 @@ std::string operator==(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator!=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) != reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -81,9 +80,7 @@ std::string operator!=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator<(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) < reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                          : "false";
 }
@@ -91,9 +88,7 @@ std::string operator<(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator>(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) > reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                          : "false";
 }
@@ -101,9 +96,7 @@ std::string operator>(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator<=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) <= reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -111,9 +104,7 @@ std::string operator<=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator>=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
-    // clang-format off
     GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    // clang-format on
     return reinterpret_cast<const void*>(lhs.p_) >= reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -127,19 +118,12 @@ struct NonCopyableNonMovable
     NonCopyableNonMovable& operator=(NonCopyableNonMovable&&) = delete;
 };
 
-namespace
-{
-// clang-format off
-GSL_SUPPRESS(f .4) // NO-FORMAT: attribute
-// clang-format on
+GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
 bool helper(not_null<int*> p) { return *p == 12; }
-// clang-format off
-GSL_SUPPRESS(f .4) // NO-FORMAT: attribute
-// clang-format on
+GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
 bool helper_const(not_null<const int*> p) { return *p == 12; }
 
 int* return_pointer() { return nullptr; }
-} // namespace
 
 TEST(notnull_tests, TestNotNullConstructors)
 {
@@ -158,12 +142,10 @@ TEST(notnull_tests, TestNotNullConstructors)
 #endif
     }
 
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. TestNotNullConstructors";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
-
     {
         // from shared pointer
         int i = 12;
@@ -175,7 +157,7 @@ TEST(notnull_tests, TestNotNullConstructors)
             std::make_shared<int>(10)); // shared_ptr<int> is nullptr assignable
 
         int* pi = nullptr;
-        EXPECT_DEATH((not_null<decltype(pi)>(pi)), expected);
+        EXPECT_DEATH((not_null<decltype(pi)>(pi)), deathstring);
     }
 
     {
@@ -232,8 +214,8 @@ TEST(notnull_tests, TestNotNullConstructors)
     {
         // from returned pointer
 
-        EXPECT_DEATH(helper(return_pointer()), expected);
-        EXPECT_DEATH(helper_const(return_pointer()), expected);
+        EXPECT_DEATH(helper(return_pointer()), deathstring);
+        EXPECT_DEATH(helper_const(return_pointer()), deathstring);
     }
 }
 
@@ -293,18 +275,17 @@ TEST(notnull_tests, TestNotNullCasting)
 
 TEST(notnull_tests, TestNotNullAssignment)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. TestNotNullAssignmentd";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
     int i = 12;
     not_null<int*> p(&i);
     EXPECT_TRUE(helper(p));
 
     int* q = nullptr;
-    EXPECT_DEATH(p = not_null<int*>(q), expected);
+    EXPECT_DEATH(p = not_null<int*>(q), deathstring);
 }
 
 TEST(notnull_tests, TestNotNullRawPointerComparison)
@@ -442,18 +423,6 @@ TEST(notnull_tests, TestNotNullConstructorTypeDeduction)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-
-        not_null x{&i};
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(not_null{&i});
-#endif
-        helper_const(not_null{&i});
-
-        EXPECT_TRUE(*x == 42);
-    }
-
     {
         int i = 42;
         int* p = &i;
@@ -465,31 +434,17 @@ TEST(notnull_tests, TestNotNullConstructorTypeDeduction)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-        const int* p = &i;
-
-        not_null x{p};
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(not_null{p});
-#endif
-        helper_const(not_null{p});
-
-        EXPECT_TRUE(*x == 42);
-    }
-
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. TestNotNullConstructorTypeDeduction";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
     {
         auto workaround_macro = []() {
             int* p1 = nullptr;
             const not_null x{p1};
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
@@ -497,14 +452,14 @@ TEST(notnull_tests, TestNotNullConstructorTypeDeduction)
             const int* p1 = nullptr;
             const not_null x{p1};
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
         int* p = nullptr;
 
-        EXPECT_DEATH(helper(not_null{p}), expected);
-        EXPECT_DEATH(helper_const(not_null{p}), expected);
+        EXPECT_DEATH(helper(not_null{p}), deathstring);
+        EXPECT_DEATH(helper_const(not_null{p}), deathstring);
     }
 
 #ifdef CONFIRM_COMPILATION_ERRORS
@@ -515,17 +470,6 @@ TEST(notnull_tests, TestNotNullConstructorTypeDeduction)
     }
 #endif
 }
-
-TEST(notnull_tests, TestVariantEmplace)
-{
-    int i = 0;
-    std::variant<std::monostate, not_null<int*>> v;
-    v.emplace<not_null<int*>>(&i);
-
-    EXPECT_FALSE(v.valueless_by_exception());
-    EXPECT_TRUE(v.index() == 1);
-    EXPECT_TRUE(std::get<not_null<int*>>(v) == &i);
-}
 #endif // #if defined(__cplusplus) && (__cplusplus >= 201703L)
 
 TEST(notnull_tests, TestMakeNotNull)
@@ -540,18 +484,6 @@ TEST(notnull_tests, TestMakeNotNull)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-
-        const auto x = make_not_null(&i);
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(make_not_null(&i));
-#endif
-        helper_const(make_not_null(&i));
-
-        EXPECT_TRUE(*x == 42);
-    }
-
     {
         int i = 42;
         int* p = &i;
@@ -563,24 +495,10 @@ TEST(notnull_tests, TestMakeNotNull)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-        const int* p = &i;
-
-        const auto x = make_not_null(p);
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(make_not_null(p));
-#endif
-        helper_const(make_not_null(p));
-
-        EXPECT_TRUE(*x == 42);
-    }
-
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. TestMakeNotNull";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
     {
         const auto workaround_macro = []() {
@@ -588,7 +506,7 @@ TEST(notnull_tests, TestMakeNotNull)
             const auto x = make_not_null(p1);
             EXPECT_TRUE(*x == 42);
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
@@ -597,52 +515,36 @@ TEST(notnull_tests, TestMakeNotNull)
             const auto x = make_not_null(p1);
             EXPECT_TRUE(*x == 42);
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
         int* p = nullptr;
 
-        EXPECT_DEATH(helper(make_not_null(p)), expected);
-        EXPECT_DEATH(helper_const(make_not_null(p)), expected);
+        EXPECT_DEATH(helper(make_not_null(p)), deathstring);
+        EXPECT_DEATH(helper_const(make_not_null(p)), deathstring);
     }
 
 #ifdef CONFIRM_COMPILATION_ERRORS
     {
-        EXPECT_DEATH(make_not_null(nullptr), expected);
-        EXPECT_DEATH(helper(make_not_null(nullptr)), expected);
-        EXPECT_DEATH(helper_const(make_not_null(nullptr)), expected);
+        EXPECT_DEATH(make_not_null(nullptr), deathstring);
+        EXPECT_DEATH(helper(make_not_null(nullptr)), deathstring);
+        EXPECT_DEATH(helper_const(make_not_null(nullptr)), deathstring);
     }
 #endif
 }
 
 TEST(notnull_tests, TestStdHash)
 {
-    {
-        int x = 42;
-        int y = 99;
-        not_null<int*> nn{&x};
-        const not_null<int*> cnn{&x};
+    int x = 42;
+    int y = 99;
+    not_null<int*> nn{&x};
+    const not_null<int*> cnn{&x};
 
-        std::hash<not_null<int*>> hash_nn;
-        std::hash<int*> hash_intptr;
+    std::hash<not_null<int*>> hash_nn;
+    std::hash<int*> hash_intptr;
 
-        EXPECT_TRUE(hash_nn(nn) == hash_intptr(&x));
-        EXPECT_FALSE(hash_nn(nn) == hash_intptr(&y));
-        EXPECT_FALSE(hash_nn(nn) == hash_intptr(nullptr));
-    }
-
-    {
-        const int x = 42;
-        const int y = 99;
-        not_null<const int*> nn{&x};
-        const not_null<const int*> cnn{&x};
-
-        std::hash<not_null<const int*>> hash_nn;
-        std::hash<const int*> hash_intptr;
-
-        EXPECT_TRUE(hash_nn(nn) == hash_intptr(&x));
-        EXPECT_FALSE(hash_nn(nn) == hash_intptr(&y));
-        EXPECT_FALSE(hash_nn(nn) == hash_intptr(nullptr));
-    }
+    EXPECT_TRUE(hash_nn(nn) == hash_intptr(&x));
+    EXPECT_FALSE(hash_nn(nn) == hash_intptr(&y));
+    EXPECT_FALSE(hash_nn(nn) == hash_intptr(nullptr));
 }

tests/owner_tests.cpp

@@ -20,7 +20,7 @@
 
 using namespace gsl;
 
-GSL_SUPPRESS(f .23) // NO-FORMAT: attribute
+GSL_SUPPRESS(f.23) // NO-FORMAT: attribute
 void f(int* i) { *i += 1; }
 
 TEST(owner_tests, basic_test)
@@ -34,10 +34,10 @@ TEST(owner_tests, basic_test)
 
 TEST(owner_tests, check_pointer_constraint)
 {
-#ifdef CONFIRM_COMPILATION_ERRORS
+    #ifdef CONFIRM_COMPILATION_ERRORS
     {
         owner<int> integerTest = 10;
         owner<std::shared_ptr<int>> sharedPtrTest(new int(10));
     }
-#endif
+    #endif
 }

tests/span_compatibility_tests.cpp

@@ -17,7 +17,7 @@
 #include <gtest/gtest.h>
 
 #include <gsl/byte> // for byte
-#include <gsl/span> // for span, span_iterator, operator==, operator!=
+#include <gsl/span>     // for span, span_iterator, operator==, operator!=
 
 #include <array>       // for array
 #include <cstddef>     // for ptrdiff_t
@@ -55,14 +55,14 @@ void ArrayConvertibilityCheck()
         EXPECT_TRUE(sp_const_nullptr_1.data() == stl_nullptr.data());
         EXPECT_TRUE(sp_const_nullptr_1.size() == 3);
 
-        gsl::span<const T* const> sp_const_nullptr_2{std::as_const(stl_nullptr)};
+        span<const T* const> sp_const_nullptr_2{std::as_const(stl_nullptr)};
         EXPECT_TRUE(sp_const_nullptr_2.data() == stl_nullptr.data());
         EXPECT_TRUE(sp_const_nullptr_2.size() == 3);
 
-        static_assert(std::is_same<decltype(gsl::span{stl_nullptr}), gsl::span<T*, 3>>::value,
+        static_assert(std::is_same<decltype(span{stl_nullptr}), span<T*, 3>>::value,
                       "std::is_same< decltype(span{stl_nullptr}), span<T*, 3>>::value");
         static_assert(
-            std::is_same<decltype(gsl::span{std::as_const(stl_nullptr)}), gsl::span<T* const, 3>>::value,
+            std::is_same<decltype(span{std::as_const(stl_nullptr)}), span<T* const, 3>>::value,
             "std::is_same< decltype(span{std::as_const(stl_nullptr)}), span<T* const, "
             "3>>::value");
     }

tests/span_ext_tests.cpp

@@ -16,27 +16,27 @@
 
 #include <gtest/gtest.h>
 
-#include <gsl/span> // for span and span_ext
 #include <gsl/util> // for narrow_cast, at
+#include <gsl/span_ext> // for operator==, operator!=, make_span
 
-#include <array>     // for array
-#include <exception> // for terminate
-#include <iostream>  // for cerr
-#include <vector>    // for vector
+#include <array>       // for array
+#include <iostream>    // for cerr
+#include <vector>      // for vector
 
 using namespace std;
 using namespace gsl;
 
-#include "deathTestCommon.h"
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
+} // namespace
 
 TEST(span_ext_test, make_span_from_pointer_length_constructor)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. from_pointer_length_constructor";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
-
     int arr[4] = {1, 2, 3, 4};
 
     {
@@ -49,7 +49,7 @@ TEST(span_ext_test, make_span_from_pointer_length_constructor)
 
     {
         int* p = nullptr;
-        auto s = make_span(p, narrow_cast<gsl::span<int>::size_type>(0));
+        auto s = make_span(p, narrow_cast<span<int>::size_type>(0));
         EXPECT_TRUE(s.size() == 0);
         EXPECT_TRUE(s.data() == nullptr);
     }
@@ -57,7 +57,7 @@ TEST(span_ext_test, make_span_from_pointer_length_constructor)
     {
         int* p = nullptr;
         auto workaround_macro = [=]() { make_span(p, 2); };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 }
 
@@ -88,293 +88,273 @@ TEST(span_ext_test, make_span_from_pointer_pointer_construction)
 }
 
 TEST(span_ext_test, make_span_from_array_constructor)
-{
-    int arr[5] = {1, 2, 3, 4, 5};
-    int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
-    int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+ {
+     int arr[5] = {1, 2, 3, 4, 5};
+     int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+     int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
 
-    {
-        const auto s = make_span(arr);
-        EXPECT_TRUE(s.size() == 5);
-        EXPECT_TRUE(s.data() == std::addressof(arr[0]));
-    }
+     {
+         const auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == 5);
+         EXPECT_TRUE(s.data() == std::addressof(arr[0]));
+     }
 
-    {
-        const auto s = make_span(std::addressof(arr2d[0]), 1);
-        EXPECT_TRUE(s.size() == 1);
-        EXPECT_TRUE(s.data() == std::addressof(arr2d[0]));
-    }
+     {
+         const auto s = make_span(std::addressof(arr2d[0]), 1);
+         EXPECT_TRUE(s.size() == 1);
+         EXPECT_TRUE(s.data() == std::addressof(arr2d[0]));
+     }
 
-    {
-        const auto s = make_span(std::addressof(arr3d[0]), 1);
-        EXPECT_TRUE(s.size() == 1);
-        EXPECT_TRUE(s.data() == std::addressof(arr3d[0]));
-    }
-}
+     {
+         const auto s = make_span(std::addressof(arr3d[0]), 1);
+         EXPECT_TRUE(s.size() == 1);
+         EXPECT_TRUE(s.data() == std::addressof(arr3d[0]));
+     }
+ }
 
-TEST(span_ext_test, make_span_from_dynamic_array_constructor)
-{
-    double(*arr)[3][4] = new double[100][3][4];
+ TEST(span_ext_test, make_span_from_dynamic_array_constructor)
+ {
+     double(*arr)[3][4] = new double[100][3][4];
 
-    {
-        auto s = make_span(&arr[0][0][0], 10);
-        EXPECT_TRUE(s.size() == 10);
-        EXPECT_TRUE(s.data() == &arr[0][0][0]);
-    }
+     {
+         auto s = make_span(&arr[0][0][0], 10);
+         EXPECT_TRUE(s.size() == 10);
+         EXPECT_TRUE(s.data() == &arr[0][0][0]);
+     }
 
-    delete[] arr;
-}
+     delete[] arr;
+ }
 
-TEST(span_ext_test, make_span_from_std_array_constructor)
-{
-    std::array<int, 4> arr = {1, 2, 3, 4};
+ TEST(span_ext_test, make_span_from_std_array_constructor)
+ {
+     std::array<int, 4> arr = {1, 2, 3, 4};
 
-    {
-        auto s = make_span(arr);
-        EXPECT_TRUE(s.size() == arr.size());
-        EXPECT_TRUE(s.data() == arr.data());
-    }
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
 
-    // This test checks for the bug found in gcc 6.1, 6.2, 6.3, 6.4, 6.5 7.1, 7.2, 7.3 - issue #590
-    {
-        gsl::span<int> s1 = make_span(arr);
+     // This test checks for the bug found in gcc 6.1, 6.2, 6.3, 6.4, 6.5 7.1, 7.2, 7.3 - issue #590
+     {
+         span<int> s1 = make_span(arr);
 
-        static gsl::span<int> s2;
-        s2 = s1;
+         static span<int> s2;
+         s2 = s1;
 
-#if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&          \
-    __GNUC_PATCHLEVEL__ == 0 && defined(__OPTIMIZE__)
-        // Known to be broken in gcc 6.4 and 6.5 with optimizations
-        // Issue in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83116
-        EXPECT_TRUE(s1.size() == 4);
-        EXPECT_TRUE(s2.size() == 0);
-#else
-        EXPECT_TRUE(s1.size() == s2.size());
-#endif
-    }
-}
+ #if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&          \
+     __GNUC_PATCHLEVEL__ == 0 && defined(__OPTIMIZE__)
+         // Known to be broken in gcc 6.4 and 6.5 with optimizations
+         // Issue in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83116
+         EXPECT_TRUE(s1.size() == 4);
+         EXPECT_TRUE(s2.size() == 0);
+ #else
+         EXPECT_TRUE(s1.size() == s2.size());
+ #endif
+     }
+ }
 
-TEST(span_ext_test, make_span_from_const_std_array_constructor)
-{
-    const std::array<int, 4> arr = {1, 2, 3, 4};
+ TEST(span_ext_test, make_span_from_const_std_array_constructor)
+ {
+     const std::array<int, 4> arr = {1, 2, 3, 4};
 
-    {
-        auto s = make_span(arr);
-        EXPECT_TRUE(s.size() == arr.size());
-        EXPECT_TRUE(s.data() == arr.data());
-    }
-}
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
+ }
 
-TEST(span_ext_test, make_span_from_std_array_const_constructor)
-{
-    std::array<const int, 4> arr = {1, 2, 3, 4};
+ TEST(span_ext_test, make_span_from_std_array_const_constructor)
+ {
+     std::array<const int, 4> arr = {1, 2, 3, 4};
 
-    {
-        auto s = make_span(arr);
-        EXPECT_TRUE(s.size() == arr.size());
-        EXPECT_TRUE(s.data() == arr.data());
-    }
-}
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
+ }
 
-TEST(span_ext_test, make_span_from_container_constructor)
-{
-    std::vector<int> v = {1, 2, 3};
-    const std::vector<int> cv = v;
+ TEST(span_ext_test, make_span_from_container_constructor)
+ {
+     std::vector<int> v = {1, 2, 3};
+     const std::vector<int> cv = v;
 
-    {
-        auto s = make_span(v);
-        EXPECT_TRUE(s.size() == v.size());
-        EXPECT_TRUE(s.data() == v.data());
+     {
+         auto s = make_span(v);
+         EXPECT_TRUE(s.size() == v.size());
+         EXPECT_TRUE(s.data() == v.data());
 
-        auto cs = make_span(cv);
-        EXPECT_TRUE(cs.size() == cv.size());
-        EXPECT_TRUE(cs.data() == cv.data());
-    }
-}
+         auto cs = make_span(cv);
+         EXPECT_TRUE(cs.size() == cv.size());
+         EXPECT_TRUE(cs.data() == cv.data());
+     }
+ }
 
-TEST(span_test, interop_with_gsl_at)
-{
-    std::vector<int> vec{1, 2, 3, 4, 5};
-    gsl::span<int> sp{vec};
+ TEST(span_test, interop_with_gsl_at)
+ {
+     int arr[5] = {1, 2, 3, 4, 5};
+     span<int> s{arr};
+     EXPECT_TRUE(at(s, 0) ==  1);
+     EXPECT_TRUE(at(s, 1) == 2);
+ }
 
-    std::vector<int> cvec{1, 2, 3, 4, 5};
-    gsl::span<int> csp{cvec};
+ TEST(span_ext_test, iterator_free_functions)
+ {
+     int a[] = {1, 2, 3, 4};
+     span<int> s{a};
 
-    for (gsl::index i = 0; i < gsl::narrow_cast<gsl::index>(vec.size()); ++i)
-    {
-        EXPECT_TRUE(&gsl::at(sp, i) == &vec[gsl::narrow_cast<size_t>(i)]);
-        EXPECT_TRUE(&gsl::at(csp, i) == &cvec[gsl::narrow_cast<size_t>(i)]);
-    }
+     EXPECT_TRUE((std::is_same<decltype(s.begin()), decltype(begin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(s.end()), decltype(end(s))>::value));
 
-    const auto terminateHandler = std::set_terminate([] {
-        std::cerr << "Expected Death. interop_with_gsl_at";
-        std::abort();
-    });
-    const auto expected = GetExpectedDeathString(terminateHandler);
+     EXPECT_TRUE((std::is_same<decltype(std::cbegin(s)), decltype(cbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(std::cend(s)), decltype(cend(s))>::value));
 
-    EXPECT_DEATH(gsl::at(sp, -1), expected);
-    EXPECT_DEATH(gsl::at(sp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
-    EXPECT_DEATH(gsl::at(csp, -1), expected);
-    EXPECT_DEATH(gsl::at(csp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
-}
+     EXPECT_TRUE((std::is_same<decltype(s.rbegin()), decltype(rbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(s.rend()), decltype(rend(s))>::value));
 
-TEST(span_ext_test, iterator_free_functions)
-{
-    int a[] = {1, 2, 3, 4};
-    gsl::span<int> s{a};
+     EXPECT_TRUE((std::is_same<decltype(std::crbegin(s)), decltype(crbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(std::crend(s)), decltype(crend(s))>::value));
 
-    EXPECT_TRUE((std::is_same<decltype(s.begin()), decltype(begin(s))>::value));
-    EXPECT_TRUE((std::is_same<decltype(s.end()), decltype(end(s))>::value));
+     EXPECT_TRUE(s.begin() == begin(s));
+     EXPECT_TRUE(s.end() == end(s));
 
-    EXPECT_TRUE((std::is_same<decltype(std::cbegin(s)), decltype(cbegin(s))>::value));
-    EXPECT_TRUE((std::is_same<decltype(std::cend(s)), decltype(cend(s))>::value));
+     EXPECT_TRUE(s.rbegin() == rbegin(s));
+     EXPECT_TRUE(s.rend() == rend(s));
 
-    EXPECT_TRUE((std::is_same<decltype(s.rbegin()), decltype(rbegin(s))>::value));
-    EXPECT_TRUE((std::is_same<decltype(s.rend()), decltype(rend(s))>::value));
+     EXPECT_TRUE(s.begin() == cbegin(s));
+     EXPECT_TRUE(s.end() == cend(s));
 
-    EXPECT_TRUE((std::is_same<decltype(std::crbegin(s)), decltype(crbegin(s))>::value));
-    EXPECT_TRUE((std::is_same<decltype(std::crend(s)), decltype(crend(s))>::value));
+     EXPECT_TRUE(s.rbegin() == crbegin(s));
+     EXPECT_TRUE(s.rend() == crend(s));
+ }
 
-    EXPECT_TRUE(s.begin() == begin(s));
-    EXPECT_TRUE(s.end() == end(s));
+ TEST(span_ext_test, ssize_free_function)
+ {
+     int a[] = {1, 2, 3, 4};
+     span<int> s{a};
 
-    EXPECT_TRUE(s.rbegin() == rbegin(s));
-    EXPECT_TRUE(s.rend() == rend(s));
+     EXPECT_FALSE((std::is_same<decltype(s.size()), decltype(ssize(s))>::value));
+     EXPECT_TRUE(s.size() == static_cast<std::size_t>(ssize(s)));
+ }
 
-    EXPECT_TRUE(s.begin() == cbegin(s));
-    EXPECT_TRUE(s.end() == cend(s));
+  TEST(span_ext_test, comparison_operators)
+ {
+     {
+         span<int> s1;
+         span<int> s2;
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
 
-    EXPECT_TRUE(s.rbegin() == crbegin(s));
-    EXPECT_TRUE(s.rend() == crend(s));
-}
+     {
+         int arr[] = {2, 1};
+         span<int> s1 = arr;
+         span<int> s2 = arr;
 
-TEST(span_ext_test, ssize_free_function)
-{
-    int a[] = {1, 2, 3, 4};
-    gsl::span<int> s{a};
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
 
-    EXPECT_FALSE((std::is_same<decltype(s.size()), decltype(ssize(s))>::value));
-    EXPECT_TRUE(s.size() == static_cast<std::size_t>(ssize(s)));
-}
+     {
+         int arr[] = {2, 1}; // bigger
 
-#ifndef GSL_KERNEL_MODE
-TEST(span_ext_test, comparison_operators)
-{
-    {
-        gsl::span<int> s1;
-        gsl::span<int> s2;
-        EXPECT_TRUE(s1 == s2);
-        EXPECT_FALSE(s1 != s2);
-        EXPECT_FALSE(s1 < s2);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s1 >= s2);
-        EXPECT_TRUE(s2 == s1);
-        EXPECT_FALSE(s2 != s1);
-        EXPECT_FALSE(s2 != s1);
-        EXPECT_TRUE(s2 <= s1);
-        EXPECT_FALSE(s2 > s1);
-        EXPECT_TRUE(s2 >= s1);
-    }
+         span<int> s1;
+         span<int> s2 = arr;
 
-    {
-        int arr[] = {2, 1};
-        gsl::span<int> s1 = arr;
-        gsl::span<int> s2 = arr;
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
 
-        EXPECT_TRUE(s1 == s2);
-        EXPECT_FALSE(s1 != s2);
-        EXPECT_FALSE(s1 < s2);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s1 >= s2);
-        EXPECT_TRUE(s2 == s1);
-        EXPECT_FALSE(s2 != s1);
-        EXPECT_FALSE(s2 < s1);
-        EXPECT_TRUE(s2 <= s1);
-        EXPECT_FALSE(s2 > s1);
-        EXPECT_TRUE(s2 >= s1);
-    }
+     {
+         int arr1[] = {1, 2};
+         int arr2[] = {1, 2};
+         span<int> s1 = arr1;
+         span<int> s2 = arr2;
 
-    {
-        int arr[] = {2, 1}; // bigger
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
 
-        gsl::span<int> s1;
-        gsl::span<int> s2 = arr;
+     {
+         int arr[] = {1, 2, 3};
 
-        EXPECT_TRUE(s1 != s2);
-        EXPECT_TRUE(s2 != s1);
-        EXPECT_FALSE(s1 == s2);
-        EXPECT_FALSE(s2 == s1);
-        EXPECT_TRUE(s1 < s2);
-        EXPECT_FALSE(s2 < s1);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s2 <= s1);
-        EXPECT_TRUE(s2 > s1);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s2 >= s1);
-        EXPECT_FALSE(s1 >= s2);
-    }
+         span<int> s1 = {&arr[0], 2}; // shorter
+         span<int> s2 = arr;          // longer
 
-    {
-        int arr1[] = {1, 2};
-        int arr2[] = {1, 2};
-        gsl::span<int> s1 = arr1;
-        gsl::span<int> s2 = arr2;
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
 
-        EXPECT_TRUE(s1 == s2);
-        EXPECT_FALSE(s1 != s2);
-        EXPECT_FALSE(s1 < s2);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s1 >= s2);
-        EXPECT_TRUE(s2 == s1);
-        EXPECT_FALSE(s2 != s1);
-        EXPECT_FALSE(s2 < s1);
-        EXPECT_TRUE(s2 <= s1);
-        EXPECT_FALSE(s2 > s1);
-        EXPECT_TRUE(s2 >= s1);
-    }
+     {
+         int arr1[] = {1, 2}; // smaller
+         int arr2[] = {2, 1}; // bigger
 
-    {
-        int arr[] = {1, 2, 3};
+         span<int> s1 = arr1;
+         span<int> s2 = arr2;
 
-        gsl::span<int> s1 = {&arr[0], 2}; // shorter
-        gsl::span<int> s2 = arr;          // longer
-
-        EXPECT_TRUE(s1 != s2);
-        EXPECT_TRUE(s2 != s1);
-        EXPECT_FALSE(s1 == s2);
-        EXPECT_FALSE(s2 == s1);
-        EXPECT_TRUE(s1 < s2);
-        EXPECT_FALSE(s2 < s1);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s2 <= s1);
-        EXPECT_TRUE(s2 > s1);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s2 >= s1);
-        EXPECT_FALSE(s1 >= s2);
-    }
-
-    {
-        int arr1[] = {1, 2}; // smaller
-        int arr2[] = {2, 1}; // bigger
-
-        gsl::span<int> s1 = arr1;
-        gsl::span<int> s2 = arr2;
-
-        EXPECT_TRUE(s1 != s2);
-        EXPECT_TRUE(s2 != s1);
-        EXPECT_FALSE(s1 == s2);
-        EXPECT_FALSE(s2 == s1);
-        EXPECT_TRUE(s1 < s2);
-        EXPECT_FALSE(s2 < s1);
-        EXPECT_TRUE(s1 <= s2);
-        EXPECT_FALSE(s2 <= s1);
-        EXPECT_TRUE(s2 > s1);
-        EXPECT_FALSE(s1 > s2);
-        EXPECT_TRUE(s2 >= s1);
-        EXPECT_FALSE(s1 >= s2);
-    }
-}
-#endif // GSL_KERNEL_MODE
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
+ }

tests/strict_notnull_tests.cpp

@@ -14,40 +14,30 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#include <gsl/pointers> // for not_null, operator<, operator<=, operator>
 #include <gtest/gtest.h>
+#include <gsl/pointers>           // for not_null, operator<, operator<=, operator>
 
-#include "deathTestCommon.h"
+namespace gsl
+{
+struct fail_fast;
+} // namespace gsl
 
 using namespace gsl;
 
-namespace
-{
-// clang-format off
-GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
-// clang-format on
+GSL_SUPPRESS(f.4)  // NO-FORMAT: attribute
 bool helper(not_null<int*> p) { return *p == 12; }
 
-// clang-format off
 GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
-// clang-format on
 bool helper_const(not_null<const int*> p) { return *p == 12; }
 
-// clang-format off
 GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
-// clang-format on
 bool strict_helper(strict_not_null<int*> p) { return *p == 12; }
 
-// clang-format off
 GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
-// clang-format on
 bool strict_helper_const(strict_not_null<const int*> p) { return *p == 12; }
 
-#ifdef CONFIRM_COMPILATION_ERRORS
 int* return_pointer() { return nullptr; }
 const int* return_pointer_const() { return nullptr; }
-#endif
-} // namespace
 
 TEST(strict_notnull_tests, TestStrictNotNull)
 {
@@ -71,28 +61,6 @@ TEST(strict_notnull_tests, TestStrictNotNull)
         EXPECT_TRUE(*snn1 == 42);
     }
 
-    {
-        // raw ptr <-> strict_not_null
-        const int x = 42;
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        strict_not_null<int*> snn = &x;
-        strict_helper(&x);
-        strict_helper_const(&x);
-        strict_helper(return_pointer());
-        strict_helper_const(return_pointer_const());
-#endif
-
-        const strict_not_null<const int*> snn1{&x};
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(snn1);
-#endif
-        helper_const(snn1);
-
-        EXPECT_TRUE(*snn1 == 42);
-    }
-
     {
         // strict_not_null -> strict_not_null
         int x = 42;
@@ -107,22 +75,6 @@ TEST(strict_notnull_tests, TestStrictNotNull)
         EXPECT_TRUE(snn1 == snn2);
     }
 
-    {
-        // strict_not_null -> strict_not_null
-        const int x = 42;
-
-        strict_not_null<const int*> snn1{&x};
-        const strict_not_null<const int*> snn2{&x};
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        strict_helper(snn1);
-#endif
-        strict_helper_const(snn1);
-        strict_helper_const(snn2);
-
-        EXPECT_TRUE(snn1 == snn2);
-    }
-
     {
         // strict_not_null -> not_null
         int x = 42;
@@ -139,24 +91,6 @@ TEST(strict_notnull_tests, TestStrictNotNull)
         EXPECT_TRUE(snn == nn2);
     }
 
-    {
-        // strict_not_null -> not_null
-        const int x = 42;
-
-        strict_not_null<const int*> snn{&x};
-
-        const not_null<const int*> nn1 = snn;
-        const not_null<const int*> nn2{snn};
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(snn);
-#endif
-        helper_const(snn);
-
-        EXPECT_TRUE(snn == nn1);
-        EXPECT_TRUE(snn == nn2);
-    }
-
     {
         // not_null -> strict_not_null
         int x = 42;
@@ -181,32 +115,6 @@ TEST(strict_notnull_tests, TestStrictNotNull)
         EXPECT_TRUE(hash_snn(snn1) == hash_snn(nn));
     }
 
-    {
-        // not_null -> strict_not_null
-        const int x = 42;
-
-        not_null<const int*> nn{&x};
-
-        const strict_not_null<const int*> snn1{nn};
-        const strict_not_null<const int*> snn2{nn};
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        strict_helper(nn);
-#endif
-        strict_helper_const(nn);
-
-        EXPECT_TRUE(snn1 == nn);
-        EXPECT_TRUE(snn2 == nn);
-
-        std::hash<strict_not_null<const int*>> hash_snn;
-        std::hash<not_null<const int*>> hash_nn;
-
-        EXPECT_TRUE(hash_nn(snn1) == hash_nn(nn));
-        EXPECT_TRUE(hash_snn(snn1) == hash_nn(nn));
-        EXPECT_TRUE(hash_nn(snn1) == hash_nn(snn2));
-        EXPECT_TRUE(hash_snn(snn1) == hash_snn(nn));
-    }
-
 #ifdef CONFIRM_COMPILATION_ERRORS
     {
         strict_not_null<int*> p{nullptr};
@@ -215,14 +123,17 @@ TEST(strict_notnull_tests, TestStrictNotNull)
 }
 
 #if defined(__cplusplus) && (__cplusplus >= 201703L)
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
+}
 
 TEST(strict_notnull_tests, TestStrictNotNullConstructorTypeDeduction)
 {
-    const auto terminateHandler = std::set_terminate([] {
+    std::set_terminate([] {
         std::cerr << "Expected Death. TestStrictNotNullConstructorTypeDeduction";
         std::abort();
     });
-    const auto expected = GetExpectedDeathString(terminateHandler);
 
     {
         int i = 42;
@@ -234,18 +145,6 @@ TEST(strict_notnull_tests, TestStrictNotNullConstructorTypeDeduction)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-
-        strict_not_null x{&i};
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(strict_not_null{&i});
-#endif
-        helper_const(strict_not_null{&i});
-
-        EXPECT_TRUE(*x == 42);
-    }
-
     {
         int i = 42;
         int* p = &i;
@@ -257,25 +156,12 @@ TEST(strict_notnull_tests, TestStrictNotNullConstructorTypeDeduction)
         EXPECT_TRUE(*x == 42);
     }
 
-    {
-        const int i = 42;
-        const int* p = &i;
-
-        strict_not_null x{p};
-#ifdef CONFIRM_COMPILATION_ERRORS
-        helper(strict_not_null{p});
-#endif
-        helper_const(strict_not_null{p});
-
-        EXPECT_TRUE(*x == 42);
-    }
-
     {
         auto workaround_macro = []() {
             int* p1 = nullptr;
             const strict_not_null x{p1};
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
@@ -283,14 +169,14 @@ TEST(strict_notnull_tests, TestStrictNotNullConstructorTypeDeduction)
             const int* p1 = nullptr;
             const strict_not_null x{p1};
         };
-        EXPECT_DEATH(workaround_macro(), expected);
+        EXPECT_DEATH(workaround_macro(), deathstring);
     }
 
     {
         int* p = nullptr;
 
-        EXPECT_DEATH(helper(strict_not_null{p}), expected);
-        EXPECT_DEATH(helper_const(strict_not_null{p}), expected);
+        EXPECT_DEATH(helper(strict_not_null{p}), deathstring);
+        EXPECT_DEATH(helper_const(strict_not_null{p}), deathstring);
     }
 
 #ifdef CONFIRM_COMPILATION_ERRORS

tests/strided_span_tests.cpp

@@ -0,0 +1,790 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <gtest/gtest.h>
+#include <gsl/byte>   // for byte
+#include <gsl/util>   // for narrow_cast
+#include <gsl/multi_span> // for strided_span, index, multi_span, strided_...
+
+#include <iostream>    // for size_t
+#include <iterator>    // for begin, end
+#include <numeric>     // for iota
+#include <type_traits> // for integral_constant<>::value, is_convertible
+#include <vector>      // for vector
+
+using namespace std;
+using namespace gsl;
+
+
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
+
+struct BaseClass
+{
+};
+struct DerivedClass : BaseClass
+{
+};
+
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
+void iterate_every_other_element(multi_span<int, dynamic_range> av)
+{
+    // pick every other element
+
+    auto length = av.size() / 2;
+#if defined(_MSC_VER) && _MSC_VER > 1800
+    auto bounds = strided_bounds<1>({length}, {2});
+#else
+    auto bounds = strided_bounds<1>(multi_span_index<1>{length}, multi_span_index<1>{2});
+#endif
+    strided_span<int, 1> strided(&av.data()[1], av.size() - 1, bounds);
+
+    EXPECT_TRUE(strided.size() == length);
+    EXPECT_TRUE(strided.bounds().index_bounds()[0] == length);
+    for (auto i = 0; i < strided.size(); ++i) {
+        EXPECT_TRUE(strided[i] == av[2 * i + 1]);
+    }
+
+    int idx = 0;
+    for (auto num : strided) {
+        EXPECT_TRUE(num == av[2 * idx + 1]);
+        idx++;
+    }
+}
+
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute // TODO: does not work
+void iterate_second_slice(multi_span<int, dynamic_range, dynamic_range, dynamic_range> av)
+{
+    const int expected[6] = {2, 3, 10, 11, 18, 19};
+    auto section = av.section({0, 1, 0}, {3, 1, 2});
+
+    for (auto i = 0; i < section.extent<0>(); ++i) {
+        for (auto j = 0; j < section.extent<1>(); ++j)
+            for (auto k = 0; k < section.extent<2>(); ++k) {
+                auto idx = multi_span_index<3>{i, j, k}; // avoid braces in the EXPECT_TRUE macro
+                EXPECT_TRUE(section[idx] == expected[2 * i + 2 * j + k]);
+            }
+    }
+
+    for (auto i = 0; i < section.extent<0>(); ++i) {
+        for (auto j = 0; j < section.extent<1>(); ++j)
+            for (auto k = 0; k < section.extent<2>(); ++k)
+                EXPECT_TRUE(section[i][j][k] == expected[2 * i + 2 * j + k]);
+    }
+
+    int i = 0;
+    for (const auto num : section) {
+        EXPECT_TRUE(num == expected[i]);
+        i++;
+    }
+}
+
+}
+
+TEST(strided_span_tests, span_section_test)
+{
+    int a[30][4][5];
+
+    const auto av = as_multi_span(a);
+    const auto sub = av.section({15, 0, 0}, gsl::multi_span_index<3>{2, 2, 2});
+    const auto subsub = sub.section({1, 0, 0}, gsl::multi_span_index<3>{1, 1, 1});
+    (void) subsub;
+}
+
+TEST(strided_span_tests, span_section)
+{
+    std::vector<int> data(5 * 10);
+    std::iota(begin(data), end(data), 0);
+    const multi_span<int, 5, 10> av = as_multi_span(multi_span<int>{data}, dim<5>(), dim<10>());
+
+    const strided_span<int, 2> av_section_1 = av.section({1, 2}, {3, 4});
+    EXPECT_TRUE(!av_section_1.empty());
+    EXPECT_TRUE((av_section_1[{0, 0}] == 12));
+    EXPECT_TRUE((av_section_1[{0, 1}] == 13));
+    EXPECT_TRUE((av_section_1[{1, 0}] == 22));
+    EXPECT_TRUE((av_section_1[{2, 3}] == 35));
+
+    const strided_span<int, 2> av_section_2 = av_section_1.section({1, 2}, {2, 2});
+    EXPECT_TRUE(!av_section_2.empty());
+    EXPECT_TRUE((av_section_2[{0, 0}] == 24));
+    EXPECT_TRUE((av_section_2[{0, 1}] == 25));
+    EXPECT_TRUE((av_section_2[{1, 0}] == 34));
+}
+
+TEST(strided_span_tests, strided_span_constructors)
+{
+    // EXPECT_TRUE stride constructor
+    {
+        int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+        const int carr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+
+        strided_span<int, 1> sav1{arr, {{9}, {1}}}; // T -> T
+        EXPECT_TRUE(sav1.bounds().index_bounds() == multi_span_index<1>{9});
+        EXPECT_TRUE(sav1.bounds().stride() == 1);
+        EXPECT_TRUE(sav1[0] == 1);
+        EXPECT_TRUE(sav1[8] == 9);
+
+        strided_span<const int, 1> sav2{carr, {{4}, {2}}}; // const T -> const T
+        EXPECT_TRUE(sav2.bounds().index_bounds() == multi_span_index<1>{4});
+        EXPECT_TRUE(sav2.bounds().strides() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav2[0] == 1);
+        EXPECT_TRUE(sav2[3] == 7);
+
+        strided_span<int, 2> sav3{arr, {{2, 2}, {6, 2}}}; // T -> const T
+        EXPECT_TRUE((sav3.bounds().index_bounds() == multi_span_index<2>{2, 2}));
+        EXPECT_TRUE((sav3.bounds().strides() == multi_span_index<2>{6, 2}));
+        EXPECT_TRUE((sav3[{0, 0}]) == 1);
+        EXPECT_TRUE((sav3[{0, 1}]) ==  3);
+        EXPECT_TRUE((sav3[{1, 0}]) == 7);
+    }
+
+    // EXPECT_TRUE multi_span constructor
+    {
+        int arr[] = {1, 2};
+
+        // From non-cv-qualified source
+        {
+            const multi_span<int> src = arr;
+
+            strided_span<int, 1> sav{src, {2, 1}};
+            EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav[1] == 2);
+
+#if defined(_MSC_VER) && _MSC_VER > 1800
+            // strided_span<const int, 1> sav_c{ {src}, {2, 1} };
+            strided_span<const int, 1> sav_c{multi_span<const int>{src},
+                                             strided_bounds<1>{2, 1}};
+#else
+            strided_span<const int, 1> sav_c{multi_span<const int>{src},
+                                             strided_bounds<1>{2, 1}};
+#endif
+            EXPECT_TRUE(sav_c.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_c.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_c[1] == 2);
+
+#if defined(_MSC_VER) && _MSC_VER > 1800
+            strided_span<volatile int, 1> sav_v{src, {2, 1}};
+#else
+            strided_span<volatile int, 1> sav_v{multi_span<volatile int>{src},
+                                                strided_bounds<1>{2, 1}};
+#endif
+            EXPECT_TRUE(sav_v.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_v.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_v[1] == 2);
+
+#if defined(_MSC_VER) && _MSC_VER > 1800
+            strided_span<const volatile int, 1> sav_cv{src, {2, 1}};
+#else
+            strided_span<const volatile int, 1> sav_cv{multi_span<const volatile int>{src},
+                                                       strided_bounds<1>{2, 1}};
+#endif
+            EXPECT_TRUE(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_cv.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_cv[1] == 2);
+        }
+
+        // From const-qualified source
+        {
+            const multi_span<const int> src{arr};
+
+            strided_span<const int, 1> sav_c{src, {2, 1}};
+            EXPECT_TRUE(sav_c.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_c.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_c[1] == 2);
+
+#if defined(_MSC_VER) && _MSC_VER > 1800
+            strided_span<const volatile int, 1> sav_cv{src, {2, 1}};
+#else
+            strided_span<const volatile int, 1> sav_cv{multi_span<const volatile int>{src},
+                                                       strided_bounds<1>{2, 1}};
+#endif
+
+            EXPECT_TRUE(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_cv.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_cv[1] == 2);
+        }
+
+        // From volatile-qualified source
+        {
+            const multi_span<volatile int> src{arr};
+
+            strided_span<volatile int, 1> sav_v{src, {2, 1}};
+            EXPECT_TRUE(sav_v.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_v.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_v[1] == 2);
+
+#if defined(_MSC_VER) && _MSC_VER > 1800
+            strided_span<const volatile int, 1> sav_cv{src, {2, 1}};
+#else
+            strided_span<const volatile int, 1> sav_cv{multi_span<const volatile int>{src},
+                                                       strided_bounds<1>{2, 1}};
+#endif
+            EXPECT_TRUE(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_cv.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_cv[1] == 2);
+        }
+
+        // From cv-qualified source
+        {
+            const multi_span<const volatile int> src{arr};
+
+            strided_span<const volatile int, 1> sav_cv{src, {2, 1}};
+            EXPECT_TRUE(sav_cv.bounds().index_bounds() == multi_span_index<1>{2});
+            EXPECT_TRUE(sav_cv.bounds().strides() == multi_span_index<1>{1});
+            EXPECT_TRUE(sav_cv[1] == 2);
+        }
+    }
+
+    // EXPECT_TRUE const-casting constructor
+    {
+        int arr[2] = {4, 5};
+
+        const multi_span<int, 2> av(arr, 2);
+        multi_span<const int, 2> av2{av};
+        EXPECT_TRUE(av2[1] == 5);
+
+        static_assert(
+            std::is_convertible<const multi_span<int, 2>, multi_span<const int, 2>>::value,
+            "ctor is not implicit!");
+
+        const strided_span<int, 1> src{arr, {2, 1}};
+        strided_span<const int, 1> sav{src};
+        EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav.bounds().stride() == 1);
+        EXPECT_TRUE(sav[1] == 5);
+
+        static_assert(
+            std::is_convertible<const strided_span<int, 1>, strided_span<const int, 1>>::value,
+            "ctor is not implicit!");
+    }
+
+    // EXPECT_TRUE copy constructor
+    {
+        int arr1[2] = {3, 4};
+        const strided_span<int, 1> src1{arr1, {2, 1}};
+        strided_span<int, 1> sav1{src1};
+
+        EXPECT_TRUE(sav1.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav1.bounds().stride() == 1);
+        EXPECT_TRUE(sav1[0] == 3);
+
+        int arr2[6] = {1, 2, 3, 4, 5, 6};
+        const strided_span<const int, 2> src2{arr2, {{3, 2}, {2, 1}}};
+        strided_span<const int, 2> sav2{src2};
+        EXPECT_TRUE((sav2.bounds().index_bounds() == multi_span_index<2>{3, 2}));
+        EXPECT_TRUE((sav2.bounds().strides() == multi_span_index<2>{2, 1}));
+        EXPECT_TRUE((sav2[{0, 0}]) ==  1);
+        EXPECT_TRUE((sav2[{2, 0}]) == 5);
+    }
+
+    // EXPECT_TRUE const-casting assignment operator
+    {
+        int arr1[2] = {1, 2};
+        int arr2[6] = {3, 4, 5, 6, 7, 8};
+
+        const strided_span<int, 1> src{arr1, {{2}, {1}}};
+        strided_span<const int, 1> sav{arr2, {{3}, {2}}};
+        strided_span<const int, 1>& sav_ref = (sav = src);
+        EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav.bounds().strides() == multi_span_index<1>{1});
+        EXPECT_TRUE(sav[0] == 1);
+        EXPECT_TRUE(&sav_ref == &sav);
+    }
+
+    // EXPECT_TRUE copy assignment operator
+    {
+        int arr1[2] = {3, 4};
+        int arr1b[1] = {0};
+        const strided_span<int, 1> src1{arr1, {2, 1}};
+        strided_span<int, 1> sav1{arr1b, {1, 1}};
+        strided_span<int, 1>& sav1_ref = (sav1 = src1);
+        EXPECT_TRUE(sav1.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav1.bounds().strides() == multi_span_index<1>{1});
+        EXPECT_TRUE(sav1[0] == 3);
+        EXPECT_TRUE(&sav1_ref == &sav1);
+
+        const int arr2[6] = {1, 2, 3, 4, 5, 6};
+        const int arr2b[1] = {0};
+        const strided_span<const int, 2> src2{arr2, {{3, 2}, {2, 1}}};
+        strided_span<const int, 2> sav2{arr2b, {{1, 1}, {1, 1}}};
+        strided_span<const int, 2>& sav2_ref = (sav2 = src2);
+        EXPECT_TRUE((sav2.bounds().index_bounds() == multi_span_index<2>{3, 2}));
+        EXPECT_TRUE((sav2.bounds().strides() == multi_span_index<2>{2, 1}));
+        EXPECT_TRUE((sav2[{0, 0}] == 1));
+        EXPECT_TRUE((sav2[{2, 0}] == 5));
+        EXPECT_TRUE(&sav2_ref == &sav2);
+    }
+}
+
+TEST(strided_span_tests, strided_span_slice)
+{
+    std::vector<int> data(5 * 10);
+    std::iota(begin(data), end(data), 0);
+    const multi_span<int, 5, 10> src =
+        as_multi_span(multi_span<int>{data}, dim<5>(), dim<10>());
+
+    const strided_span<int, 2> sav{src, {{5, 10}, {10, 1}}};
+#ifdef CONFIRM_COMPILATION_ERRORS
+    const strided_span<const int, 2> csav{{src}, {{5, 10}, {10, 1}}};
+#endif
+    const strided_span<const int, 2> csav{multi_span<const int, 5, 10>{src},
+                                          {{5, 10}, {10, 1}}};
+
+    strided_span<int, 1> sav_sl = sav[2];
+    EXPECT_TRUE(sav_sl[0] == 20);
+    EXPECT_TRUE(sav_sl[9] == 29);
+
+    strided_span<const int, 1> csav_sl = sav[3];
+    EXPECT_TRUE(csav_sl[0] == 30);
+    EXPECT_TRUE(csav_sl[9] == 39);
+
+    EXPECT_TRUE(sav[4][0] == 40);
+    EXPECT_TRUE(sav[4][9] == 49);
+}
+
+TEST(strided_span_tests, strided_span_column_major)
+{
+    // strided_span may be used to accommodate more peculiar
+    // use cases, such as column-major multidimensional array
+    // (aka. "FORTRAN" layout).
+
+    int cm_array[3 * 5] = {1, 4, 7, 10, 13, 2, 5, 8, 11, 14, 3, 6, 9, 12, 15};
+    strided_span<int, 2> cm_sav{cm_array, {{5, 3}, {1, 5}}};
+
+    // Accessing elements
+    EXPECT_TRUE((cm_sav[{0, 0}] == 1));
+    EXPECT_TRUE((cm_sav[{0, 1}] == 2));
+    EXPECT_TRUE((cm_sav[{1, 0}] == 4));
+    EXPECT_TRUE((cm_sav[{4, 2}] == 15));
+
+    // Slice
+    strided_span<int, 1> cm_sl = cm_sav[3];
+
+    EXPECT_TRUE(cm_sl[0] == 10);
+    EXPECT_TRUE(cm_sl[1] == 11);
+    EXPECT_TRUE(cm_sl[2] == 12);
+
+    // Section
+    strided_span<int, 2> cm_sec = cm_sav.section({2, 1}, {3, 2});
+
+    EXPECT_TRUE((cm_sec.bounds().index_bounds() == multi_span_index<2>{3, 2}));
+    EXPECT_TRUE((cm_sec[{0, 0}] == 8));
+    EXPECT_TRUE((cm_sec[{0, 1}] == 9));
+    EXPECT_TRUE((cm_sec[{1, 0}] == 11));
+    EXPECT_TRUE((cm_sec[{2, 1}] == 15));
+}
+
+TEST(strided_span_tests, strided_span_bounds)
+{
+    int arr[] = {0, 1, 2, 3};
+    multi_span<int> av(arr);
+
+    std::set_terminate([] {
+        std::cerr << "Expected Death. strided_span_bounds";
+        std::abort();
+    });
+
+    {
+        // incorrect sections
+
+        EXPECT_DEATH(av.section(0, 0)[0], deathstring);
+        EXPECT_DEATH(av.section(1, 0)[0], deathstring);
+        EXPECT_DEATH(av.section(1, 1)[1], deathstring);
+
+        EXPECT_DEATH(av.section(2, 5), deathstring);
+        EXPECT_DEATH(av.section(5, 2), deathstring);
+        EXPECT_DEATH(av.section(5, 0), deathstring);
+        EXPECT_DEATH(av.section(0, 5), deathstring);
+        EXPECT_DEATH(av.section(5, 5), deathstring);
+    }
+
+    {
+        // zero stride
+        strided_span<int, 1> sav{av, {{4}, {}}};
+        EXPECT_TRUE(sav[0] == 0);
+        EXPECT_TRUE(sav[3] == 0);
+        EXPECT_DEATH(sav[4], deathstring);
+    }
+
+    {
+        // zero extent
+        strided_span<int, 1> sav{av, {{}, {1}}};
+        EXPECT_DEATH(sav[0], deathstring);
+    }
+
+    {
+        // zero extent and stride
+        strided_span<int, 1> sav{av, {{}, {}}};
+        EXPECT_DEATH(sav[0], deathstring);
+    }
+
+    {
+        // strided array ctor with matching strided bounds
+        strided_span<int, 1> sav{arr, {4, 1}};
+        EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{4});
+        EXPECT_TRUE(sav[3] == 3);
+        EXPECT_DEATH(sav[4], deathstring);
+    }
+
+    {
+        // strided array ctor with smaller strided bounds
+        strided_span<int, 1> sav{arr, {2, 1}};
+        EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav[1] == 1);
+        EXPECT_DEATH(sav[2], deathstring);
+    }
+
+    {
+        // strided array ctor with fitting irregular bounds
+        strided_span<int, 1> sav{arr, {2, 3}};
+        EXPECT_TRUE(sav.bounds().index_bounds() == multi_span_index<1>{2});
+        EXPECT_TRUE(sav[0] == 0);
+        EXPECT_TRUE(sav[1] == 3);
+        EXPECT_DEATH(sav[2], deathstring);
+    }
+
+    {
+        // bounds cross data boundaries - from static arrays
+        EXPECT_DEATH((strided_span<int, 1>{arr, {3, 2}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{arr, {3, 3}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{arr, {4, 5}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{arr, {5, 1}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{arr, {5, 5}}), deathstring);
+    }
+
+    {
+        // bounds cross data boundaries - from array view
+        EXPECT_DEATH((strided_span<int, 1>{av, {3, 2}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av, {3, 3}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av, {4, 5}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av, {5, 1}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av, {5, 5}}), deathstring);
+    }
+
+    {
+        // bounds cross data boundaries - from dynamic arrays
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 4, {3, 2}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 4, {3, 3}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 4, {4, 5}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 4, {5, 1}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 4, {5, 5}}), deathstring);
+        EXPECT_DEATH((strided_span<int, 1>{av.data(), 2, {2, 2}}), deathstring);
+    }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    {
+        strided_span<int, 1> sav0{av.data(), {3, 2}};
+        strided_span<int, 1> sav1{arr, {1}};
+        strided_span<int, 1> sav2{arr, {1, 1, 1}};
+        strided_span<int, 1> sav3{av, {1}};
+        strided_span<int, 1> sav4{av, {1, 1, 1}};
+        strided_span<int, 2> sav5{av.as_multi_span(dim<2>(), dim<2>()), {1}};
+        strided_span<int, 2> sav6{av.as_multi_span(dim<2>(), dim<2>()), {1, 1, 1}};
+        strided_span<int, 2> sav7{av.as_multi_span(dim<2>(), dim<2>()),
+                                  {{1, 1}, {1, 1}, {1, 1}}};
+
+        multi_span_index<1> index{0, 1};
+        strided_span<int, 1> sav8{arr, {1, {1, 1}}};
+        strided_span<int, 1> sav9{arr, {{1, 1}, {1, 1}}};
+        strided_span<int, 1> sav10{av, {1, {1, 1}}};
+        strided_span<int, 1> sav11{av, {{1, 1}, {1, 1}}};
+        strided_span<int, 2> sav12{av.as_multi_span(dim<2>(), dim<2>()), {{1}, {1}}};
+        strided_span<int, 2> sav13{av.as_multi_span(dim<2>(), dim<2>()), {{1}, {1, 1, 1}}};
+        strided_span<int, 2> sav14{av.as_multi_span(dim<2>(), dim<2>()), {{1, 1, 1}, {1}}};
+    }
+#endif
+}
+
+TEST(strided_span_tests, strided_span_type_conversion)
+{
+    int arr[] = {0, 1, 2, 3};
+    multi_span<int> av(arr);
+
+    std::set_terminate([] {
+        std::cerr << "Expected Death. strided_span_type_conversion";
+        std::abort();
+    });
+
+    {
+        strided_span<int, 1> sav{av.data(), av.size(), {av.size() / 2, 2}};
+#ifdef CONFIRM_COMPILATION_ERRORS
+        strided_span<long, 1> lsav1 = sav.as_strided_span<long, 1>();
+#endif
+    }
+    {
+        strided_span<int, 1> sav{av, {av.size() / 2, 2}};
+#ifdef CONFIRM_COMPILATION_ERRORS
+        strided_span<long, 1> lsav1 = sav.as_strided_span<long, 1>();
+#endif
+    }
+
+    multi_span<const byte, dynamic_range> bytes = as_bytes(av);
+
+    // retype strided array with regular strides - from raw data
+    {
+        strided_bounds<2> bounds{{2, bytes.size() / 4}, {bytes.size() / 2, 1}};
+        strided_span<const byte, 2> sav2{bytes.data(), bytes.size(), bounds};
+        strided_span<const int, 2> sav3 = sav2.as_strided_span<const int>();
+        EXPECT_TRUE(sav3[0][0] == 0);
+        EXPECT_TRUE(sav3[1][0] == 2);
+        EXPECT_DEATH(sav3[1][1], deathstring);
+        EXPECT_DEATH(sav3[0][1], deathstring);
+    }
+
+    // retype strided array with regular strides - from multi_span
+    {
+        strided_bounds<2> bounds{{2, bytes.size() / 4}, {bytes.size() / 2, 1}};
+        multi_span<const byte, 2, dynamic_range> bytes2 =
+            as_multi_span(bytes, dim<2>(), dim(bytes.size() / 2));
+        strided_span<const byte, 2> sav2{bytes2, bounds};
+        strided_span<int, 2> sav3 = sav2.as_strided_span<int>();
+        EXPECT_TRUE(sav3[0][0] == 0);
+        EXPECT_TRUE(sav3[1][0] == 2);
+        EXPECT_DEATH(sav3[1][1], deathstring);
+        EXPECT_DEATH(sav3[0][1], deathstring);
+    }
+
+    // retype strided array with not enough elements - last dimension of the array is too small
+    {
+        strided_bounds<2> bounds{{4, 2}, {4, 1}};
+        multi_span<const byte, 2, dynamic_range> bytes2 =
+            as_multi_span(bytes, dim<2>(), dim(bytes.size() / 2));
+        strided_span<const byte, 2> sav2{bytes2, bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+
+    // retype strided array with not enough elements - strides are too small
+    {
+        strided_bounds<2> bounds{{4, 2}, {2, 1}};
+        multi_span<const byte, 2, dynamic_range> bytes2 =
+            as_multi_span(bytes, dim<2>(), dim(bytes.size() / 2));
+        strided_span<const byte, 2> sav2{bytes2, bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+
+    // retype strided array with not enough elements - last dimension does not divide by the new
+    // typesize
+    {
+        strided_bounds<2> bounds{{2, 6}, {4, 1}};
+        multi_span<const byte, 2, dynamic_range> bytes2 =
+            as_multi_span(bytes, dim<2>(), dim(bytes.size() / 2));
+        strided_span<const byte, 2> sav2{bytes2, bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+
+    // retype strided array with not enough elements - strides does not divide by the new
+    // typesize
+    {
+        strided_bounds<2> bounds{{2, 1}, {6, 1}};
+        multi_span<const byte, 2, dynamic_range> bytes2 =
+            as_multi_span(bytes, dim<2>(), dim(bytes.size() / 2));
+        strided_span<const byte, 2> sav2{bytes2, bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+
+    // retype strided array with irregular strides - from raw data
+    {
+        strided_bounds<1> bounds{bytes.size() / 2, 2};
+        strided_span<const byte, 1> sav2{bytes.data(), bytes.size(), bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+
+    // retype strided array with irregular strides - from multi_span
+    {
+        strided_bounds<1> bounds{bytes.size() / 2, 2};
+        strided_span<const byte, 1> sav2{bytes, bounds};
+        EXPECT_DEATH(sav2.as_strided_span<int>(), deathstring);
+    }
+}
+
+TEST(strided_span_tests, empty_strided_spans)
+{
+    std::set_terminate([] {
+        std::cerr << "Expected Death. empty_strided_spans";
+        std::abort();
+    });
+
+    {
+        multi_span<int, 0> empty_av(nullptr);
+        strided_span<int, 1> empty_sav{empty_av, {0, 1}};
+
+        EXPECT_TRUE(empty_sav.bounds().index_bounds() == multi_span_index<1>{0});
+        EXPECT_TRUE(empty_sav.empty());
+        EXPECT_DEATH(empty_sav[0], deathstring);
+        EXPECT_DEATH(empty_sav.begin()[0], deathstring);
+        EXPECT_DEATH(empty_sav.cbegin()[0], deathstring);
+
+        for (const auto& v : empty_sav) {
+            (void) v;
+            EXPECT_TRUE(false);
+        }
+    }
+
+    {
+        strided_span<int, 1> empty_sav{nullptr, 0, {0, 1}};
+
+        EXPECT_TRUE(empty_sav.bounds().index_bounds() == multi_span_index<1>{0});
+        EXPECT_DEATH(empty_sav[0], deathstring);
+        EXPECT_DEATH(empty_sav.begin()[0], deathstring);
+        EXPECT_DEATH(empty_sav.cbegin()[0], deathstring);
+
+        for (const auto& v : empty_sav) {
+            (void) v;
+            EXPECT_TRUE(false);
+        }
+    }
+}
+
+TEST(strided_span_tests, strided_span_section_iteration)
+{
+    int arr[8] = {4, 0, 5, 1, 6, 2, 7, 3};
+
+    // static bounds
+    {
+        multi_span<int, 8> av(arr, 8);
+        iterate_every_other_element(av);
+    }
+
+    // dynamic bounds
+    {
+        multi_span<int, dynamic_range> av(arr, 8);
+        iterate_every_other_element(av);
+    }
+}
+
+TEST(strided_span_tests, dynamic_strided_span_section_iteration)
+{
+    auto arr = new int[8];
+    for (int i = 0; i < 4; ++i) {
+        arr[2 * i] = 4 + i;
+        arr[2 * i + 1] = i;
+    }
+
+    auto av = as_multi_span(arr, 8);
+    iterate_every_other_element(av);
+
+    delete[] arr;
+}
+
+TEST(strided_span_tests, strided_span_section_iteration_3d)
+{
+    int arr[3][4][2]{};
+    for (auto i = 0; i < 3; ++i) {
+        for (auto j = 0; j < 4; ++j)
+            for (auto k = 0; k < 2; ++k) arr[i][j][k] = 8 * i + 2 * j + k;
+    }
+
+    {
+        multi_span<int, 3, 4, 2> av = arr;
+        iterate_second_slice(av);
+    }
+}
+
+TEST(strided_span_tests, dynamic_strided_span_section_iteration_3d)
+{
+    const auto height = 12, width = 2;
+    const auto size = height * width;
+
+    auto arr = new int[static_cast<std::size_t>(size)];
+    for (auto i = 0; i < size; ++i) {
+        arr[i] = i;
+    }
+
+    {
+        auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim<4>(), dim<2>());
+        iterate_second_slice(av);
+    }
+
+    {
+        auto av = as_multi_span(as_multi_span(arr, 24), dim(3), dim<4>(), dim<2>());
+        iterate_second_slice(av);
+    }
+
+    {
+        auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim(4), dim<2>());
+        iterate_second_slice(av);
+    }
+
+    {
+        auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim<4>(), dim(2));
+        iterate_second_slice(av);
+    }
+    delete[] arr;
+}
+
+TEST(strided_span_tests, strided_span_conversion)
+{
+    std::set_terminate([] {
+        std::cerr << "Expected Death. strided_span_conversion";
+        std::abort();
+    });
+
+    // get an multi_span of 'c' values from the list of X's
+
+    struct X
+    {
+        int a;
+        int b;
+        int c;
+    };
+
+    X arr[4] = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {9, 10, 11}};
+
+    int s = sizeof(int) / sizeof(byte);
+    auto d2 = 3 * s;
+    auto d1 = narrow_cast<int>(sizeof(int)) * 12 / d2;
+
+    // convert to 4x12 array of bytes
+    auto av = as_multi_span(as_bytes(as_multi_span(&arr[0], 4)), dim(d1), dim(d2));
+
+    EXPECT_TRUE(av.bounds().index_bounds()[0] == 4);
+    EXPECT_TRUE(av.bounds().index_bounds()[1] == 12);
+
+    // get the last 4 columns
+    auto section = av.section({0, 2 * s}, {4, s}); // { { arr[0].c[0], arr[0].c[1], arr[0].c[2],
+                                                   // arr[0].c[3] } , { arr[1].c[0], ... } , ...
+                                                   // }
+
+    // convert to array 4x1 array of integers
+    auto cs = section.as_strided_span<int>(); // { { arr[0].c }, {arr[1].c } , ... }
+
+    EXPECT_TRUE(cs.bounds().index_bounds()[0] == 4);
+    EXPECT_TRUE(cs.bounds().index_bounds()[1] == 1);
+
+    // transpose to 1x4 array
+    strided_bounds<2> reverse_bounds{
+        {cs.bounds().index_bounds()[1], cs.bounds().index_bounds()[0]},
+        {cs.bounds().strides()[1], cs.bounds().strides()[0]}};
+
+    strided_span<int, 2> transposed{cs.data(), cs.bounds().total_size(), reverse_bounds};
+
+    // slice to get a one-dimensional array of c's
+    strided_span<int, 1> result = transposed[0];
+
+    EXPECT_TRUE(result.bounds().index_bounds()[0] == 4);
+    EXPECT_DEATH(result.bounds().index_bounds()[1], deathstring);
+
+    int i = 0;
+    for (auto& num : result) {
+        EXPECT_TRUE(num == arr[i].c);
+        i++;
+    }
+}

tests/utils_tests.cpp

@@ -16,15 +16,14 @@
 
 #include <gtest/gtest.h>
 
+#include <gsl/util>     // finally, narrow_cast
+#include <gsl/narrow>   // for narrow, narrowing_error
 #include <algorithm>   // for move
-#include <complex>
-#include <cstddef>     // for std::ptrdiff_t
-#include <cstdint>     // for uint32_t, int32_t
 #include <functional>  // for reference_wrapper, _Bind_helper<>::type
-#include <gsl/narrow>  // for narrow, narrowing_error
-#include <gsl/util>    // finally, narrow_cast
 #include <limits>      // for numeric_limits
+#include <stdint.h>    // for uint32_t, int32_t
 #include <type_traits> // for is_same
+#include <cstddef>     // for std::ptrdiff_t
 
 using namespace gsl;
 
@@ -33,7 +32,8 @@ namespace
 void f(int& i) { i += 1; }
 static int j = 0;
 void g() { j += 1; }
-} // namespace
+}
+
 
 TEST(utils_tests, sanity_check_for_gsl_index_typedef)
 {
@@ -96,7 +96,7 @@ TEST(utils_tests, finally_function_with_bind)
 {
     int i = 0;
     {
-        auto _ = finally([&i] { return f(i); });
+        auto _ = finally(std::bind(&f, std::ref(i)));
         EXPECT_TRUE(i == 0);
     }
     EXPECT_TRUE(i == 1);
@@ -112,16 +112,6 @@ TEST(utils_tests, finally_function_ptr)
     EXPECT_TRUE(j == 1);
 }
 
-TEST(utils_tests, finally_function)
-{
-    j = 0;
-    {
-        auto _ = finally(g);
-        EXPECT_TRUE(j == 0);
-    }
-    EXPECT_TRUE(j == 1);
-}
-
 TEST(utils_tests, narrow_cast)
 {
     int n = 120;
@@ -133,7 +123,6 @@ TEST(utils_tests, narrow_cast)
     EXPECT_TRUE(uc == 44);
 }
 
-#ifndef GSL_KERNEL_MODE
 TEST(utils_tests, narrow)
 {
     int n = 120;
@@ -155,11 +144,4 @@ TEST(utils_tests, narrow)
 
     n = -42;
     EXPECT_THROW(narrow<unsigned>(n), narrowing_error);
-
-    EXPECT_TRUE(
-        narrow<std::complex<float>>(std::complex<double>(4, 2)) == std::complex<float>(4, 2));
-    EXPECT_THROW(narrow<std::complex<float>>(std::complex<double>(4.2)), narrowing_error);
-
-    EXPECT_TRUE(narrow<int>(float(1)) == 1);
 }
-#endif // GSL_KERNEL_MODE