Merge branch 'feature/issue-26-nofix' into feature/issue-26

Add "cxxstd" json field. The "cxxstd" json field is being added to ea…

.github/workflows/ci.yml

@@ -0,0 +1,197 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - develop
+      - feature/**
+
+env:
+  UBSAN_OPTIONS: print_stacktrace=1
+
+jobs:
+  posix:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - toolset: gcc-4.8
+            cxxstd: "03,11"
+            os: ubuntu-16.04
+            install: g++-4.8
+          - toolset: gcc-4.9
+            cxxstd: "03,11"
+            os: ubuntu-16.04
+            install: g++-4.9
+          - toolset: gcc-5
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-16.04
+          - toolset: gcc-6
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-16.04
+            install: g++-6
+          - toolset: gcc-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+          - toolset: gcc-8
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-18.04
+          - toolset: gcc-9
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-18.04
+          - toolset: gcc-10
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-18.04
+          - toolset: clang
+            compiler: clang++-3.5
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-3.5
+          - toolset: clang
+            compiler: clang++-3.6
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-3.6
+          - toolset: clang
+            compiler: clang++-3.7
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-3.7
+          - toolset: clang
+            compiler: clang++-3.8
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-3.8
+          - toolset: clang
+            compiler: clang++-3.9
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-3.9
+          - toolset: clang
+            compiler: clang++-4.0
+            cxxstd: "03,11,14"
+            os: ubuntu-16.04
+            install: clang-4.0
+          - toolset: clang
+            compiler: clang++-5.0
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-16.04
+            install: clang-5.0
+          - toolset: clang
+            compiler: clang++-6.0
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+          - toolset: clang
+            compiler: clang++-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+            install: clang-7
+          - toolset: clang
+            compiler: clang++-8
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-9
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-10
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            cxxstd: "03,11,14,17,2a"
+            os: macos-10.15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt install ${{matrix.install}}
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+          ./bootstrap.sh
+          ./b2 -d0 headers
+
+      - name: Create user-config.jam
+        if: matrix.compiler
+        run: |
+          echo "using ${{matrix.toolset}} : : ${{matrix.compiler}} ;" > ~/user-config.jam
+
+      - name: Run tests
+        run: |
+          cd ../boost-root
+          ./b2 -j3 libs/$LIBRARY/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} variant=debug,release
+
+  windows:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - toolset: msvc-14.1
+            cxxstd: "14,17,latest"
+            addrmd: 32,64
+            os: windows-2016
+          - toolset: msvc-14.2
+            cxxstd: "14,17,latest"
+            addrmd: 32,64
+            os: windows-2019
+          - toolset: gcc
+            cxxstd: "03,11,14,17,2a"
+            addrmd: 64
+            os: windows-2019
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+          cmd /c bootstrap
+          b2 -d0 headers
+
+      - name: Run tests
+        shell: cmd
+        run: |
+          cd ../boost-root
+          b2 -j3 libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release

.travis.yml

@@ -1,11 +1,9 @@
-# Copyright 2016-2019 Peter Dimov
+# Copyright 2016-2021 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
 language: cpp
 
-sudo: false
-
 dist: xenial
 
 branches:
@@ -25,8 +23,14 @@ matrix:
 
   include:
     - os: linux
-      compiler: g++
-      env: TOOLSET=gcc COMPILER=g++ CXXSTD=11
+      compiler: g++-4.8
+      env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=11
+      addons:
+        apt:
+          packages:
+            - g++-4.8
+          sources:
+            - ubuntu-toolchain-r-test
 
     - os: linux
       compiler: g++-4.9
@@ -89,12 +93,13 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
-      compiler: g++-8
-      env: UBSAN=1 TOOLSET=gcc COMPILER=g++-8 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1 LINKFLAGS=-fuse-ld=gold
+      dist: bionic
+      compiler: g++-10
+      env: UBSAN=1 TOOLSET=gcc COMPILER=g++-10 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1 LINKFLAGS=-fuse-ld=gold
       addons:
         apt:
           packages:
-            - g++-8
+            - g++-10
           sources:
             - ubuntu-toolchain-r-test
 
@@ -160,6 +165,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-5.0
       env: TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=11,14,1z
       addons:
@@ -170,6 +176,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-6.0
       env: TOOLSET=clang COMPILER=clang++-6.0 CXXSTD=11,14,17
       addons:
@@ -180,6 +187,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-7
       env: TOOLSET=clang COMPILER=clang++-7 CXXSTD=11,14,17,2a
       addons:
@@ -188,9 +196,10 @@ matrix:
             - clang-7
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-7
+            - llvm-toolchain-bionic-7
 
     - os: linux
+      dist: bionic
       compiler: clang++-8
       env: TOOLSET=clang COMPILER=clang++-8 CXXSTD=11,14,17,2a
       addons:
@@ -199,10 +208,10 @@ matrix:
             - clang-8
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-8
+            - llvm-toolchain-bionic-8
 
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: clang++-9
       env: TOOLSET=clang COMPILER=clang++-9 CXXSTD=11,14,17,2a
       addons:
@@ -211,19 +220,47 @@ matrix:
             - clang-9
           sources:
             - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
               key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux
-      compiler: clang++-8
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-8 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
+      dist: bionic
+      compiler: clang++-10
+      env: TOOLSET=clang COMPILER=clang++-10 CXXSTD=11,14,17,2a
       addons:
         apt:
           packages:
-            - clang-8
+            - clang-10
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-8
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
+
+    - os: linux
+      dist: bionic
+      compiler: clang++-11
+      env: TOOLSET=clang COMPILER=clang++-11 CXXSTD=11,14,17,2a
+      addons:
+        apt:
+          packages:
+            - clang-11
+          sources:
+            - ubuntu-toolchain-r-test
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-11 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
+
+    - os: linux
+      dist: bionic
+      compiler: clang++-12
+      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-12 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
+      addons:
+        apt:
+          packages:
+            - clang-12
+          sources:
+            - ubuntu-toolchain-r-test
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-12 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux
       dist: trusty
@@ -235,18 +272,14 @@ matrix:
             - libc++-dev
 
     - os: linux
-      dist: trusty
+      dist: bionic
       compiler: clang++-libc++
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=11,14,1z UBSAN_OPTIONS=print_stacktrace=1
+      env: TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=11,14,17,2a
       addons:
         apt:
           packages:
             - libc++-dev
 
-    - os: osx
-      compiler: clang++
-      env: TOOLSET=clang COMPILER=clang++ CXXSTD=11,14,1z
-
     - os: osx
       compiler: clang++
       env: UBSAN=1 TOOLSET=clang COMPILER=clang++ CXXSTD=11,14,1z UBSAN_OPTIONS=print_stacktrace=1
@@ -259,7 +292,6 @@ matrix:
         - ctest --output-on-failure -R boost_variant2
 
     - os: linux
-      compiler: g++
       env: CMAKE_SUBDIR_TEST=1
       install:
         - BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
@@ -276,8 +308,9 @@ matrix:
     - os: linux
       env: CMAKE_INSTALL_TEST=1
       script:
+        - pip install --user cmake
         - mkdir __build__ && cd __build__
-        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES="variant2;config;mp11" -DCMAKE_INSTALL_PREFIX=~/.local ..
+        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES=variant2 -DCMAKE_INSTALL_PREFIX=~/.local ..
         - cmake --build . --target install
         - cd ../libs/variant2/test/cmake_install_test && mkdir __build__ && cd __build__
         - cmake -DCMAKE_INSTALL_PREFIX=~/.local ..

CMakeLists.txt

@@ -17,13 +17,6 @@ target_link_libraries(boost_variant2
     Boost::mp11
 )
 
-if(BOOST_SUPERPROJECT_VERSION)
-
-  include(BoostInstall)
-  boost_install(TARGETS boost_variant2 HEADER_DIRECTORY include/)
-
-endif()
-
 if(BUILD_TESTING)
 
   add_subdirectory(test)

appveyor.yml

@@ -1,4 +1,4 @@
-# Copyright 2016-2018 Peter Dimov
+# Copyright 2016-2020 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
@@ -20,7 +20,15 @@ environment:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
       TOOLSET: msvc-14.1
       ADDRMD: 32,64
-      CXXSTD: 14,17
+      CXXSTD: 14,17,latest
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOOLSET: clang-win
+      ADDRMD: 64
+      CXXSTD: 14,17,latest
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      TOOLSET: msvc-14.2
+      ADDRMD: 32,64
+      CXXSTD: 14,17,latest
 
 install:
   - set BOOST_BRANCH=develop
@@ -28,8 +36,6 @@ install:
   - cd ..
   - git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
   - cd boost-root
-  - git submodule update --init tools/build
-  - git submodule update --init libs/config
   - git submodule update --init tools/boostdep
   - xcopy /s /e /q %APPVEYOR_BUILD_FOLDER% libs\variant2\
   - python tools/boostdep/depinst/depinst.py variant2
@@ -41,4 +47,4 @@ build: off
 test_script:
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
-  - b2 libs/variant2/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release
+  - b2 -j3 libs/variant2/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release

doc/variant2/changelog.adoc

@@ -1,5 +1,5 @@
 ////
-Copyright 2019 Peter Dimov
+Copyright 2019-2021 Peter Dimov
 
 Distributed under the Boost Software License, Version 1.0.
 
@@ -11,6 +11,23 @@ http://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_
 
+## Changes in 1.76.0
+
+* Improved generated code for the double buffered case.
+
+## Changes in 1.74.0
+
+* Added support for derived types in `visit`
+* Improved compilation performance for many (hundreds of) alternatives.
+* Added support for `visit<R>`
+
+## Changes in 1.73.0
+
+* Added support for `std::hash`, `boost::hash`.
+* `variant<T...>` is now trivial when all types in `T...` are trivial.
+  This improves performance by enabling it to be passed to, and returned
+  from, functions in registers.
+
 ## Changes in 1.71.0
 
 After the Boost formal review, the implementation has been

doc/variant2/design.adoc

@@ -169,8 +169,6 @@ The main differences between this implementation and `std::variant` are:
   `variant<int, float>` is provided as the member function `subset<U...>`.
   (This operation can throw if the current state of the variant cannot be
   represented.)
-* `variant<T...>` is not (yet) trivial when all contained types are trivial,
-   as mandated by {cpp}17.
 * The {cpp}20 additions and changes to `std::variant` have not yet been
   implemented.
 

doc/variant2/reference.adoc

@@ -134,7 +134,7 @@ template<class... T>
 
 // visit
 
-template<class F, class... V>
+template<class R = /*unspecified*/, class F, class... V>
   constexpr /*see below*/ visit(F&& f, V&&... v);
 
 // monostate
@@ -490,8 +490,8 @@ template<size_t I, class... A>
 +
 Requires: :: `I < sizeof...(T)`.
 Effects:  ::
-  Destroys the currently contained value, then initializes a new contained
-  value as if using the expression `Ti(std::forward<A>(a)...)`.
+  Initializes a new contained value as if using the expression
+  `Ti(std::forward<A>(a)...)`, then destroys the currently contained value.
 Ensures:  :: `index() == I`.
 Returns:  :: A reference to the new contained value.
 Throws:   ::
@@ -511,8 +511,8 @@ template<size_t I, class V, class... A>
 +
 Requires: :: `I < sizeof...(T)`.
 Effects:  ::
-  Destroys the currently contained value, then initializes a new contained
-  value as if using the expression `Ti(il, std::forward<A>(a)...)`.
+  Initializes a new contained value as if using the expression
+  `Ti(il, std::forward<A>(a)...)`, then destroys the currently contained value.
 Ensures:  :: `index() == I`.
 Returns:  :: A reference to the new contained value.
 Throws:   ::
@@ -838,7 +838,7 @@ Returns: ::
 ### visit
 
 ```
-template<class F, class... V>
+template<class R = /*unspecified*/, class F, class... V>
   constexpr /*see below*/ visit(F&& f, V&&... v);
 ```
 [none]
@@ -846,6 +846,10 @@ template<class F, class... V>
 +
 Returns: :: `std::forward<F>(f)(get<I>(std::forward<V>(v))...)`, where
   `I...` is `v.index()...`.
+Remarks: :: If `R` is given explicitly, as in `visit<int>`, the return
+  type is `R`. Otherwise, it's deduced from `F`. All possible applications
+  of `F` to the variant alternatives must have the same return type for
+  this deduction to succeed.
 
 ### swap
 

meta/libraries.json

@@ -5,10 +5,11 @@
         "Peter Dimov"
     ],
     "maintainers": [
-        "Peter Dimov <pdimov -at- pdimov.com>"
+        "Peter Dimov <pdimov -at- gmail.com>"
     ],
     "description": "A never-valueless, strong guarantee implementation of std::variant.",
     "category": [
         "Containers", "Data"
-    ]
+    ],
+    "cxxstd": "11"
 }

test/CMakeLists.txt

@@ -6,6 +6,6 @@ include(BoostTestJamfile OPTIONAL RESULT_VARIABLE HAVE_BOOST_TEST)
 
 if(HAVE_BOOST_TEST)
 
-boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core)
+boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core Boost::container_hash)
 
 endif()

test/Jamfile

@@ -12,7 +12,7 @@ import ../../config/checks/config : requires ;
 project
   : default-build
 
-    <warnings>all
+    <warnings>extra
 
   : requirements
 
@@ -29,16 +29,16 @@ run variant_size.cpp ;
 run variant_alternative.cpp ;
 
 run variant_holds_alternative.cpp ;
-compile variant_holds_alternative_cx.cpp ;
+compile variant_holds_alternative_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_get_by_index.cpp ;
-compile variant_get_by_index_cx.cpp ;
+compile variant_get_by_index_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_get_by_type.cpp ;
-compile variant_get_by_type_cx.cpp ;
+compile variant_get_by_type_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_default_construct.cpp ;
-compile variant_default_construct_cx.cpp ;
+compile variant_default_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_copy_construct.cpp ;
 compile variant_copy_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
@@ -47,13 +47,13 @@ run variant_move_construct.cpp ;
 compile variant_move_construct_cx.cpp : [ requires cxx14_constexpr ] ;
 
 run variant_value_construct.cpp ;
-compile variant_value_construct_cx.cpp ;
+compile variant_value_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_in_place_index_construct.cpp ;
-compile variant_in_place_index_construct_cx.cpp ;
+compile variant_in_place_index_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_in_place_type_construct.cpp ;
-compile variant_in_place_type_construct_cx.cpp ;
+compile variant_in_place_type_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_copy_assign.cpp ;
 compile variant_copy_assign_cx.cpp : [ requires cxx14_constexpr ] ;
@@ -99,9 +99,25 @@ local NX =
     ;
 
 run variant_get_by_index.cpp throw_exception.cpp : : : $(NX) : variant_get_by_index_nx ;
-compile variant_get_by_index_cx.cpp : $(NX) : variant_get_by_index_cx_nx ;
+compile variant_get_by_index_cx.cpp : $(NX) <toolset>msvc-14.0:<build>no : variant_get_by_index_cx_nx ;
 
 run variant_get_by_type.cpp throw_exception.cpp : : : $(NX) : variant_get_by_type_nx ;
-compile variant_get_by_type_cx.cpp : $(NX) : variant_get_by_type_cx_nx ;
+compile variant_get_by_type_cx.cpp : $(NX) <toolset>msvc-14.0:<build>no : variant_get_by_type_cx_nx ;
 
 run variant_subset.cpp throw_exception.cpp : : : $(NX) : variant_subset_nx ;
+
+run variant_hash.cpp ;
+
+run variant_trivial.cpp ;
+run variant_special.cpp ;
+
+run variant_visit_derived.cpp ;
+
+run variant_many_types.cpp ;
+
+run variant_visit_r.cpp : : :
+    <toolset>gcc,<target-os>windows:<variant>release
+    <toolset>gcc,<target-os>cygwin:<variant>release
+    ;
+
+compile variant_derived_construct.cpp ;

test/variant_copy_construct.cpp

@@ -9,6 +9,8 @@
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <type_traits>
 #include <utility>
 #include <string>
@@ -48,12 +50,21 @@ struct Y
     Y( Y const& ) = delete;
 };
 
+struct D
+{
+    ~D() {}
+};
+
+inline bool operator==( D, D ) { return true; }
+
 template<class V> static void test( V const & v )
 {
     V v2( v );
 
     BOOST_TEST_EQ( v.index(), v2.index() );
     BOOST_TEST( v == v2 );
+
+    BOOST_TEST_TRAIT_TRUE((std::is_copy_constructible<V>));
 }
 
 int main()
@@ -115,6 +126,12 @@ int main()
         test( v );
     }
 
+#if !BOOST_WORKAROUND( __GNUC__, < 5 )
+
+    test( variant<D>() );
+
+#endif
+
     {
         BOOST_TEST_TRAIT_TRUE((std::is_nothrow_copy_constructible<variant<int>>));
         BOOST_TEST_TRAIT_TRUE((std::is_nothrow_copy_constructible<variant<int const>>));

test/variant_derived_construct.cpp

@@ -0,0 +1,33 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+
+using namespace boost::variant2;
+
+template<class... T> class X: variant<T...>
+{
+    using base = variant<T...>;
+    using base::base;
+};
+
+struct Y
+{
+    Y( Y const& rhs ) = default;
+
+    template<class T> Y( T const& t )
+    {
+        t.bar();
+    }
+};
+
+int main()
+{
+    using W = X<int, double, Y>;
+
+    W a( 1 );
+    W b( a );
+
+    (void)b;
+}

test/variant_emplace_index.cpp

@@ -57,6 +57,60 @@ STATIC_ASSERT( !std::is_nothrow_move_constructible<X2>::value );
 STATIC_ASSERT( !std::is_nothrow_copy_assignable<X2>::value );
 STATIC_ASSERT( !std::is_nothrow_move_assignable<X2>::value );
 
+struct Y1
+{
+    int v = 1;
+
+    Y1() = default;
+    Y1(Y1 const&) = delete;
+    Y1(Y1&&) = delete;
+};
+
+STATIC_ASSERT( !std::is_copy_constructible<Y1>::value );
+STATIC_ASSERT( !std::is_move_constructible<Y1>::value );
+
+struct Y2
+{
+    int v = 2;
+
+    Y2() = default;
+    Y2(Y2 const&) = delete;
+    Y2(Y2&&) = delete;
+};
+
+STATIC_ASSERT( !std::is_copy_constructible<Y2>::value );
+STATIC_ASSERT( !std::is_move_constructible<Y2>::value );
+
+struct Z1
+{
+    static int instances;
+
+    int v = 1;
+
+    Z1() { ++instances; }
+    ~Z1() { --instances; }
+
+    Z1(Z1 const&) = delete;
+    Z1(Z1&&) = delete;
+};
+
+int Z1::instances = 0;
+
+struct Z2
+{
+    static int instances;
+
+    int v = 2;
+
+    Z2() { ++instances; }
+    ~Z2() { --instances; }
+
+    Z2(Z2 const&) = delete;
+    Z2(Z2&&) = delete;
+};
+
+int Z2::instances = 0;
+
 int main()
 {
     {
@@ -177,5 +231,62 @@ int main()
         BOOST_TEST_EQ( get<0>(v).v, 4 );
     }
 
+    {
+        variant<Y1, Y2> v;
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+
+        v.emplace<0>();
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+
+        v.emplace<1>();
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v).v, 2 );
+
+        v.emplace<1>();
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v).v, 2 );
+
+        v.emplace<0>();
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+    }
+
+    {
+        variant<Z1, Z2> v;
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+        BOOST_TEST_EQ( Z1::instances, 1 );
+        BOOST_TEST_EQ( Z2::instances, 0 );
+
+        v.emplace<0>();
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+        BOOST_TEST_EQ( Z1::instances, 1 );
+        BOOST_TEST_EQ( Z2::instances, 0 );
+
+        v.emplace<1>();
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v).v, 2 );
+        BOOST_TEST_EQ( Z1::instances, 0 );
+        BOOST_TEST_EQ( Z2::instances, 1 );
+
+        v.emplace<1>();
+        BOOST_TEST_EQ( v.index(), 1 );
+        BOOST_TEST_EQ( get<1>(v).v, 2 );
+        BOOST_TEST_EQ( Z1::instances, 0 );
+        BOOST_TEST_EQ( Z2::instances, 1 );
+
+        v.emplace<0>();
+        BOOST_TEST_EQ( v.index(), 0 );
+        BOOST_TEST_EQ( get<0>(v).v, 1 );
+        BOOST_TEST_EQ( Z1::instances, 1 );
+        BOOST_TEST_EQ( Z2::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( Z1::instances, 0 );
+    BOOST_TEST_EQ( Z2::instances, 0 );
+
     return boost::report_errors();
 }

test/variant_eq_ne.cpp

@@ -88,5 +88,12 @@ int main()
         BOOST_TEST_NOT( v1 != v2 );
     }
 
+    {
+        variant<monostate> v1, v2;
+
+        BOOST_TEST( v1 == v2 );
+        BOOST_TEST_NOT( v1 != v2 );
+    }
+
     return boost::report_errors();
 }

test/variant_eq_ne_cx.cpp

@@ -93,6 +93,13 @@ int main()
         STATIC_ASSERT( !(v1 == v2) );
         STATIC_ASSERT( !(v1 != v2) );
     }
+
+    {
+        constexpr variant<monostate> v1, v2;
+
+        STATIC_ASSERT( v1 == v2 );
+        STATIC_ASSERT( !(v1 != v2) );
+    }
 }
 
 #endif

test/variant_get_by_index.cpp

@@ -6,6 +6,12 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined( __clang__ ) && defined( __has_warning )
+# if __has_warning( "-Wdeprecated-volatile" )
+#  pragma clang diagnostic ignored "-Wdeprecated-volatile"
+# endif
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>

test/variant_get_by_type.cpp

@@ -6,6 +6,12 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined( __clang__ ) && defined( __has_warning )
+# if __has_warning( "-Wdeprecated-volatile" )
+#  pragma clang diagnostic ignored "-Wdeprecated-volatile"
+# endif
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>

test/variant_hash.cpp

@@ -0,0 +1,73 @@
+
+// Copyright 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER)
+# pragma warning( disable: 4244 ) // conversion from int to float, possible loss of data
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/container_hash/hash.hpp>
+#include <boost/config/workaround.hpp>
+
+using namespace boost::variant2;
+
+template<template<class...> class Hash, class T1, class T2, class T3> void test()
+{
+    variant<T1, T2, T3> v1( in_place_index_t<0>{} );
+    std::size_t h1 = Hash<decltype(v1)>()( v1 );
+
+    variant<T1, T2, T3> v2( in_place_index_t<1>{} );
+    std::size_t h2 = Hash<decltype(v2)>()( v2 );
+
+    variant<T1, T2, T3> v3( in_place_index_t<2>{} );
+    std::size_t h3 = Hash<decltype(v3)>()( v3 );
+
+    BOOST_TEST_NE( h1, h2 );
+    BOOST_TEST_NE( h1, h3 );
+    BOOST_TEST_NE( h2, h3 );
+}
+
+template<template<class...> class Hash, class T> void test2()
+{
+    variant<T> v1( 0 );
+    std::size_t h1 = Hash<decltype(v1)>()( v1 );
+
+    variant<T> v2( 1 );
+    std::size_t h2 = Hash<decltype(v2)>()( v2 );
+
+    variant<T> v3( 2 );
+    std::size_t h3 = Hash<decltype(v3)>()( v3 );
+
+    BOOST_TEST_NE( h1, h2 );
+    BOOST_TEST_NE( h1, h3 );
+    BOOST_TEST_NE( h2, h3 );
+}
+
+struct X {};
+
+int main()
+{
+    test<std::hash, monostate, monostate, monostate>();
+    test<std::hash, int, int, float>();
+
+    test<boost::hash, monostate, monostate, monostate>();
+    test<boost::hash, int, int, float>();
+
+    test2<std::hash, int>();
+    test2<std::hash, float>();
+
+    test2<boost::hash, int>();
+    test2<boost::hash, float>();
+
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1910) && ( !defined(_LIBCPP_STD_VER) || _LIBCPP_STD_VER > 11 )
+
+    BOOST_TEST_TRAIT_FALSE(( detail::is_hash_enabled<X> ));
+
+#endif
+
+    return boost::report_errors();
+}

test/variant_in_place_index_construct_cx.cpp

@@ -7,11 +7,8 @@
 // http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/variant2/variant.hpp>
-#include <boost/core/lightweight_test.hpp>
-#include <boost/core/lightweight_test_trait.hpp>
-#include <type_traits>
-#include <utility>
-#include <string>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 
 using namespace boost::variant2;
 
@@ -108,9 +105,17 @@ int main()
         STATIC_ASSERT( v.index() == 4 );
     }
 
+#if BOOST_WORKAROUND(BOOST_GCC, >= 100000 && BOOST_GCC < 110000)
+
+    // no idea why this fails on g++ 10
+
+#else
+
     {
         constexpr variant<int, int, float, float, X, X> v( in_place_index_t<5>{}, 0, 0 );
 
         STATIC_ASSERT( v.index() == 5 );
     }
+
+#endif
 }

test/variant_in_place_type_construct_cx.cpp

@@ -7,6 +7,8 @@
 // http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 
 using namespace boost::variant2;
 
@@ -100,6 +102,12 @@ int main()
         STATIC_ASSERT( holds_alternative<X>(v) );
     }
 
+#if BOOST_WORKAROUND(BOOST_GCC, >= 100000 && BOOST_GCC < 110000)
+
+    // no idea why this fails on g++ 10
+
+#else
+
     {
         constexpr variant<int, int, float, float, X> v( in_place_type_t<X>{}, 0, 0 );
 
@@ -107,4 +115,6 @@ int main()
 
         STATIC_ASSERT( holds_alternative<X>(v) );
     }
+
+#endif
 }

test/variant_lt_gt.cpp

@@ -81,5 +81,14 @@ int main()
         BOOST_TEST_NOT( v1 >= v2 );
     }
 
+    {
+        variant<monostate> v1, v2;
+
+        BOOST_TEST_NOT( v1 < v2 );
+        BOOST_TEST_NOT( v1 > v2 );
+        BOOST_TEST( v1 <= v2 );
+        BOOST_TEST( v1 >= v2 );
+    }
+
     return boost::report_errors();
 }

test/variant_lt_gt_cx.cpp

@@ -86,6 +86,15 @@ int main()
         STATIC_ASSERT( !(v1 <= v2) );
         STATIC_ASSERT( !(v1 >= v2) );
     }
+
+    {
+        constexpr variant<monostate> v1, v2;
+
+        STATIC_ASSERT( !(v1 < v2) );
+        STATIC_ASSERT( !(v1 > v2) );
+        STATIC_ASSERT( v1 <= v2 );
+        STATIC_ASSERT( v1 >= v2 );
+    }
 }
 
 #endif

test/variant_many_types.cpp

@@ -0,0 +1,109 @@
+
+// Copyright 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER)
+# pragma warning( disable: 4503 ) // decorated name length exceeded
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/mp11.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::mp11;
+
+template<class I> struct X
+{
+    static int const value = I::value;
+    int v_;
+};
+
+template<class I> int const X<I>::value;
+
+template<class I> struct Y
+{
+    static int const value = I::value;
+    int v_;
+
+    Y() = default;
+    Y( Y const& ) = default;
+
+    explicit Y( int v ): v_( v ) {}
+
+    Y& operator=( Y const& ) noexcept = default;
+
+    Y& operator=( Y&& r ) noexcept
+    {
+        v_ = r.v_;
+        return *this;
+    }
+};
+
+template<class I> int const Y<I>::value;
+
+template<class I> struct Z
+{
+    static int const value = I::value;
+    int v_;
+
+    ~Z() {}
+};
+
+template<class I> int const Z<I>::value;
+
+template<class V> struct F1
+{
+    template<class T> void operator()( T ) const
+    {
+        int const i = T::value;
+
+        T t{ i * 2 };
+
+        using boost::variant2::get;
+
+        {
+            V v( t );
+
+            BOOST_TEST_EQ( v.index(), i );
+            BOOST_TEST_EQ( get<i>( v ).v_, t.v_ );
+            BOOST_TEST_EQ( get<T>( v ).v_, t.v_ );
+        }
+
+        {
+            V const v( t );
+
+            BOOST_TEST_EQ( v.index(), i );
+            BOOST_TEST_EQ( get<i>( v ).v_, t.v_ );
+            BOOST_TEST_EQ( get<T>( v ).v_, t.v_ );
+        }
+
+        {
+            V v;
+
+            v = t;
+
+            BOOST_TEST_EQ( v.index(), i );
+            BOOST_TEST_EQ( get<i>( v ).v_, t.v_ );
+            BOOST_TEST_EQ( get<T>( v ).v_, t.v_ );
+        }
+    }
+};
+
+template<class V> void test()
+{
+    mp_for_each<V>( F1<V>() );
+}
+
+int main()
+{
+    int const N = 32;
+
+    using V = mp_rename<mp_iota_c<N>, boost::variant2::variant>;
+
+    test< mp_transform<X, V> >();
+    test< mp_transform<Y, V> >();
+    test< mp_transform<Z, V> >();
+
+    return boost::report_errors();
+}

test/variant_special.cpp

@@ -0,0 +1,103 @@
+// Copyright 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+# pragma warning(disable: 4503) // decorated name length exceeded
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+
+#include <boost/mp11.hpp>
+using namespace boost::mp11;
+
+//
+
+using namespace boost::variant2;
+
+struct D
+{
+    ~D() noexcept {}
+};
+
+struct CC1
+{
+    CC1( CC1 const& ) {}
+};
+
+struct CC2
+{
+    CC2( CC2 const& ) = delete;
+};
+
+struct MC1
+{
+    MC1( MC1 && ) {}
+};
+
+struct MC2
+{
+    MC2( MC2 && ) = delete;
+};
+
+struct CA1
+{
+    CA1& operator=( CA1 const& ) { return *this; }
+};
+
+struct CA2
+{
+    CA2& operator=( CA2 const& ) = delete;
+};
+
+struct MA1
+{
+    MA1& operator=( MA1 && ) { return *this; }
+};
+
+struct MA2
+{
+    MA2& operator=( MA2 && ) = delete;
+};
+
+struct test
+{
+    template<class... T> void operator()( mp_list<T...> ) const noexcept
+    {
+        using U = mp_inherit<T...>;
+
+#if !BOOST_WORKAROUND( __GNUC__, < 5 )
+
+        BOOST_TEST_EQ( std::is_copy_constructible<variant<U>>::value, std::is_copy_constructible<U>::value );
+        BOOST_TEST_EQ( std::is_nothrow_copy_constructible<variant<U>>::value, std::is_nothrow_copy_constructible<U>::value );
+
+#endif
+
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1910)
+
+        BOOST_TEST_EQ( std::is_move_constructible<variant<U>>::value, std::is_move_constructible<U>::value );
+
+#else
+
+        BOOST_TEST_GE( std::is_move_constructible<variant<U>>::value, std::is_move_constructible<U>::value );
+
+#endif
+
+        BOOST_TEST_EQ( std::is_nothrow_move_constructible<variant<U>>::value, std::is_nothrow_move_constructible<U>::value );
+
+        BOOST_TEST_EQ( std::is_copy_assignable<variant<U>>::value, std::is_copy_constructible<U>::value && std::is_copy_assignable<U>::value );
+        BOOST_TEST_EQ( std::is_nothrow_copy_assignable<variant<U>>::value, std::is_nothrow_copy_constructible<U>::value && std::is_copy_assignable<U>::value );
+
+        BOOST_TEST_EQ( std::is_move_assignable<variant<U>>::value, std::is_move_constructible<U>::value && std::is_move_assignable<U>::value );
+        BOOST_TEST_EQ( std::is_nothrow_move_assignable<variant<U>>::value, std::is_nothrow_move_constructible<U>::value && std::is_move_assignable<U>::value );
+    }
+};
+
+int main()
+{
+    mp_for_each< mp_power_set< mp_list<D, CC1, CC2, MC1, MC2, CA1, CA2, MA1, MA2> > >( test() );
+    return boost::report_errors();
+}

test/variant_trivial.cpp

@@ -0,0 +1,95 @@
+// Copyright 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+# pragma warning(disable: 4503) // decorated name length exceeded
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+
+#include <boost/mp11.hpp>
+using namespace boost::mp11;
+
+//
+
+struct D
+{
+    ~D() noexcept {}
+};
+
+struct CC1
+{
+    CC1( CC1 const& ) noexcept {}
+};
+
+struct CC2
+{
+    CC2( CC2 const& ) = delete;
+};
+
+struct MC1
+{
+    MC1( MC1 && ) noexcept {}
+};
+
+struct MC2
+{
+    MC2( MC2 && ) = delete;
+};
+
+struct CA1
+{
+    CA1& operator=( CA1 const& ) noexcept { return *this; }
+};
+
+struct CA2
+{
+    CA2& operator=( CA2 const& ) = delete;
+};
+
+struct MA1
+{
+    MA1& operator=( MA1 && ) noexcept { return *this; }
+};
+
+struct MA2
+{
+    MA2& operator=( MA2 && ) = delete;
+};
+
+using namespace boost::variant2;
+namespace v2d = boost::variant2::detail;
+
+struct test
+{
+    template<class... T> void operator()( mp_list<T...> ) const noexcept
+    {
+        using U = mp_inherit<T...>;
+
+#if !BOOST_WORKAROUND( __GNUC__, < 5 )
+
+        BOOST_TEST_EQ( v2d::is_trivially_copy_constructible<variant<U>>::value, v2d::is_trivially_copy_constructible<U>::value );
+        BOOST_TEST_EQ( v2d::is_trivially_copy_assignable<variant<U>>::value, std::is_trivially_destructible<U>::value && v2d::is_trivially_copy_constructible<U>::value && v2d::is_trivially_copy_assignable<U>::value );
+
+#endif
+
+        BOOST_TEST_EQ( std::is_trivially_destructible<variant<U>>::value, std::is_trivially_destructible<U>::value );
+
+#if !BOOST_WORKAROUND(BOOST_LIBSTDCXX_VERSION, < 50000)
+
+        BOOST_TEST_EQ( v2d::is_trivially_move_constructible<variant<U>>::value, v2d::is_trivially_move_constructible<U>::value );
+        BOOST_TEST_EQ( v2d::is_trivially_move_assignable<variant<U>>::value, std::is_trivially_destructible<U>::value && v2d::is_trivially_move_constructible<U>::value && v2d::is_trivially_move_assignable<U>::value );
+
+#endif
+    }
+};
+
+int main()
+{
+    mp_for_each< mp_power_set< mp_list<D, CC1, CC2, MC1, MC2, CA1, CA2, MA1, MA2> > >( test() );
+    return boost::report_errors();
+}

test/variant_visit.cpp

@@ -37,6 +37,10 @@ struct F
 
 int main()
 {
+    {
+        BOOST_TEST_EQ( (visit( []{ return 5; } )), 5 );
+    }
+
     {
         variant<int> v( 1 );
 

test/variant_visit_derived.cpp

@@ -0,0 +1,57 @@
+
+// Copyright 2017, 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER)
+# pragma warning( disable: 4244 ) // conversion from float to int, possible loss of data
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+#include <utility>
+
+struct X: boost::variant2::variant<int, float>
+{
+#if BOOST_WORKAROUND( BOOST_MSVC, < 1930 )
+
+    template<class T> explicit X( T&& t ): variant( std::forward<T>( t ) ) {};
+
+#else
+
+    using variant::variant;
+
+#endif
+};
+
+template<class... T> struct Y: boost::variant2::variant<T...>
+{
+    using boost::variant2::variant<T...>::variant;
+};
+
+int main()
+{
+    {
+        X v1( 1 );
+        X const v2( 3.14f );
+
+        BOOST_TEST_EQ( (visit( []( int x1, float x2 ){ return (int)(x1 * 1000) + (int)(x2 * 100); }, v1, v2 )), 1314 );
+
+        visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, v1, v2 );
+        visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, std::move(v1), std::move(v2) );
+    }
+
+    {
+        Y<int, float> v1( 1 );
+        Y<int, float> const v2( 3.14f );
+
+        BOOST_TEST_EQ( (visit( []( int x1, float x2 ){ return (int)(x1 * 1000) + (int)(x2 * 100); }, v1, v2 )), 1314 );
+
+        visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, v1, v2 );
+        visit( []( int x1, float x2 ){ BOOST_TEST_EQ( x1, 1 ); BOOST_TEST_EQ( x2, 3.14f ); }, std::move(v1), std::move(v2) );
+    }
+
+    return boost::report_errors();
+}

test/variant_visit_r.cpp

@@ -0,0 +1,98 @@
+
+// Copyright 2017 Peter Dimov.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER)
+# pragma warning( disable: 4244 ) // conversion from float to int, possible loss of data
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::variant2;
+
+struct F1
+{
+    template<class T1> T1 operator()( T1 t1 ) const
+    {
+        return t1;
+    }
+};
+
+struct F2
+{
+    template<class T1, class T2> auto operator()( T1 t1, T2 t2 ) const -> decltype( t1 + t2 )
+    {
+        return t1 + t2;
+    }
+};
+
+struct F3
+{
+    template<class T1, class T2, class T3> auto operator()( T1 t1, T2 t2, T3 t3 ) const -> decltype( t1 + t2 + t3 )
+    {
+        return t1 + t2 + t3;
+    }
+};
+
+struct F4
+{
+    template<class T1, class T2, class T3, class T4> auto operator()( T1 t1, T2 t2, T3 t3, T4 t4 ) const -> decltype( t1 + t2 + t3 + t4 )
+    {
+        return t1 + t2 + t3 + t4;
+    }
+};
+
+int main()
+{
+    {
+        BOOST_TEST_EQ( (visit<int>( []{ return 3.14f; } )), 3 );
+    }
+
+    {
+        variant<int, float> v( 1 );
+
+        BOOST_TEST_EQ( visit<int>( F1(), v ), 1 );
+        BOOST_TEST_EQ( visit<float>( F1(), v ), 1.0f );
+    }
+
+    {
+        variant<int, float> const v( 3.14f );
+
+        BOOST_TEST_EQ( visit<int>( F1(), v ), 3 );
+        BOOST_TEST_EQ( visit<float>( F1(), v ), 3.14f );
+    }
+
+    {
+        variant<int, float> v1( 1 );
+        variant<int, float> const v2( 3.14f );
+
+        BOOST_TEST_EQ( visit<int>( F2(), v1, v2 ), 4 );
+        BOOST_TEST_EQ( visit<float>( F2(), v1, v2 ), 1 + 3.14f );
+    }
+
+    {
+        variant<int, float, double> v1( 1 );
+        variant<int, float, double> const v2( 3.14f );
+        variant<int, float, double> v3( 6.28 );
+
+        BOOST_TEST_EQ( visit<int>( F3(), v1, v2, v3 ), 10 );
+        BOOST_TEST_EQ( visit<float>( F3(), v1, v2, v3 ), static_cast<float>( 1 + 3.14f + 6.28 ) );
+    }
+
+    {
+        variant<int, float, double, char> v1( 1 );
+        variant<int, float, double, char> const v2( 3.14f );
+        variant<int, float, double, char> v3( 6.28 );
+        variant<int, float, double, char> const v4( 'A' );
+
+        BOOST_TEST_EQ( visit<int>( F4(), v1, v2, v3, v4 ), 10 + 'A' );
+        BOOST_TEST_EQ( visit<float>( F4(), v1, v2, v3, v4 ), static_cast<float>( 1 + 3.14f + 6.28 + 'A' ) );
+    }
+
+    return boost::report_errors();
+}