From dc78cf182521692e52e34711a27ada19c81dd22c Mon Sep 17 00:00:00 2001
From: Antony Polukhin <antoshkka@gmail.com>
Date: Mon, 12 May 2025 17:35:17 +0300
Subject: [PATCH] Implement initial version of C++20 module `boost.type_index`
 (#15)

`#include <boost/type_index...` is now implicitly does `import boost.type_index` if the modules are supported
All the library internals now have unconditional module level linkage.

Significant differences from https://anarthal.github.io/cppblog/modules3:
* `BOOST_TYPE_INDEX_USE_STD_MODULE` macro switch for `import std;` / `includes` while building module. This allows to use module in C++20 and even without usable  `std` module.
---
 .github/workflows/ci.yml                      | 63 +++++++++++++++++--
 CMakeLists.txt                                | 28 +++++++--
 doc/type_index.qbk                            | 36 ++++++++++-
 include/boost/type_index.hpp                  | 10 ++-
 include/boost/type_index/ctti_type_index.hpp  | 14 ++++-
 .../detail/compile_time_type_info.hpp         |  4 +-
 include/boost/type_index/detail/config.hpp    | 32 ++++++++++
 .../type_index/detail/ctti_register_class.hpp |  8 +++
 .../type_index/detail/stl_register_class.hpp  |  8 +++
 include/boost/type_index/runtime_cast.hpp     |  2 +
 .../runtime_cast/boost_shared_ptr_cast.hpp    | 26 +++++---
 .../runtime_cast/detail/runtime_cast_impl.hpp |  2 +
 .../type_index/runtime_cast/pointer_cast.hpp  | 12 +++-
 .../runtime_cast/reference_cast.hpp           | 17 ++++-
 .../runtime_cast/register_runtime_class.hpp   | 11 ++++
 .../runtime_cast/std_shared_ptr_cast.hpp      | 13 ++++
 include/boost/type_index/stl_type_index.hpp   | 21 ++++++-
 .../boost/type_index/type_index_facade.hpp    | 17 ++++-
 modules/boost_type_index.cppm                 | 55 ++++++++++++++++
 modules/usage_sample.cpp                      | 18 ++++++
 modules/usage_test_mu1.cpp                    | 13 ++++
 modules/usage_test_mu2.cpp                    | 16 +++++
 test/Jamfile.v2                               |  4 +-
 test/cmake_subdir_test/CMakeLists.txt         | 52 +++++++++++++++
 test/compare_ctti_stl.cpp                     |  9 +--
 test/type_index_test.cpp                      | 21 ++++---
 26 files changed, 469 insertions(+), 43 deletions(-)
 create mode 100644 include/boost/type_index/detail/config.hpp
 create mode 100644 modules/boost_type_index.cppm
 create mode 100644 modules/usage_sample.cpp
 create mode 100644 modules/usage_test_mu1.cpp
 create mode 100644 modules/usage_test_mu2.cpp
 create mode 100644 test/cmake_subdir_test/CMakeLists.txt

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bf1ac1d..e84b089 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,10 +49,10 @@ jobs:
             compiler: clang++-14
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-22.04
-          - toolset: clang
-            compiler: clang++-10
-            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+          - toolset: clang-19
+            cxxstd: "20,23"
+            os: ubuntu-24.04
+            install: clang-19 llvm-19 libclang-rt-19-dev libc++-19-dev libc++abi-19-dev clang-tools-19
 
     runs-on: ${{matrix.os}}
 
@@ -88,6 +88,31 @@ jobs:
           ./b2 -d0 headers
           ./b2 -j4 variant=debug tools/inspect/build
 
+      - name: Run modules tests wihtout 'import std;'
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/type_index
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -GNinja -DCMAKE_CXX_COMPILER=clang++-19 ../test/cmake_subdir_test/
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
+
+      - name: Run modules tests
+        if: false
+        #if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/type_index
+          mkdir build_module
+          cd build_module
+          cmake -DBUILD_TESTING=1 -DBOOST_USE_MODULES=1 -DCMAKE_CXX_COMPILER=clang++-19 -DCMAKE_CXX_FLAGS=-stdlib=libc++ -DCMAKE_EXE_LINKER_FLAGS=-stdlib=libc++ -DCMAKE_CXX_STANDARD=23 -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
+
       - name: Run tests
         run: |
           cd ../boost-root
@@ -175,6 +200,36 @@ jobs:
           cmd /c bootstrap
           b2 -d0 headers
 
+      - name: Run modules tests
+        if: ${{matrix.toolset == 'msvc-14.3'}}
+        shell: cmd
+        run: |
+          choco install --no-progress ninja
+          call "C:/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Auxiliary/Build/vcvarsall.bat" x64
+          cd ../boost-root/libs/type_index
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -DCMAKE_CXX_STANDARD=23 -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest --no-tests=error -V
+          cd ..
+          rm -rf build_module
+
+      - name: Run modules tests without 'import std;'
+        if: ${{matrix.toolset == 'msvc-14.3'}}
+        shell: cmd
+        run: |
+          choco install --no-progress ninja
+          call "C:/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Auxiliary/Build/vcvarsall.bat" x64
+          cd ../boost-root/libs/type_index
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -DCMAKE_CXX_STANDARD=20 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest --no-tests=error -V
+          cd ..
+          rm -rf build_module
+
       - name: Run tests
         shell: cmd
         run: |
diff --git a/CMakeLists.txt b/CMakeLists.txt
index beb1d06..ed0601e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,17 +3,35 @@
 # Distributed under the Boost Software License, Version 1.0.
 # https://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...3.20)
+cmake_minimum_required(VERSION 3.5...3.31)
 
 project(boost_type_index VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
-add_library(boost_type_index INTERFACE)
+if (BOOST_USE_MODULES)
+    add_library(boost_type_index)
+    target_sources(boost_type_index PUBLIC
+        FILE_SET modules_public TYPE CXX_MODULES FILES modules/boost_type_index.cppm
+    )
+
+    target_compile_features(boost_type_index PUBLIC cxx_std_20)
+    target_compile_definitions(boost_type_index PUBLIC BOOST_USE_MODULES)
+    if (CMAKE_CXX_COMPILER_IMPORT_STD)
+        target_compile_definitions(boost_type_index PRIVATE BOOST_TYPE_INDEX_USE_STD_MODULE)
+        message(STATUS "Using `import std;`")
+    else()
+        message(STATUS "`import std;` is not awailable")
+    endif()
+    set(__scope PUBLIC)
+else()
+    add_library(boost_type_index INTERFACE)
+    set(__scope INTERFACE)
+endif()
+
+target_include_directories(boost_type_index ${__scope} include)
 add_library(Boost::type_index ALIAS boost_type_index)
 
-target_include_directories(boost_type_index INTERFACE include)
-
 target_link_libraries(boost_type_index
-  INTERFACE
+  ${__scope}
     Boost::config
     Boost::container_hash
     Boost::core
diff --git a/doc/type_index.qbk b/doc/type_index.qbk
index d6e9062..55294b9 100644
--- a/doc/type_index.qbk
+++ b/doc/type_index.qbk
@@ -1,6 +1,6 @@
 [library Boost.TypeIndex
     [quickbook 1.6]
-    [version 4.1]
+    [version 4.2]
     [copyright 2012-2025 Antony Polukhin]
     [category Language Features Emulation]
     [license
@@ -314,6 +314,40 @@ Sometimes there may be a need to create your own type info system. This may be u
 
 [endsect]
 
+[section C++20 module]
+
+[caution C++20 module support is on early stage, targets, flags and behavior may change in the future]
+
+If using modern CMake define CMake option `-DBOOST_USE_MODULES=1` to build a C++20 module and
+make the `Boost::type_index` CMake target provide it. After that an explicit usage of C++20 module `boost.type_index` is allowed:
+
+[import ../modules/usage_sample.cpp]
+[type_index_module_example]
+
+The `Boost::type_index` CMake target gives an ability to mix includes and imports of the library in different translation units. Moreover,
+if `BOOST_USE_MODULES` macro is defined then all the `boost/type_index/...` includes implicilty do `import boost.type_index;` to give all the
+benifits of modules without changing the existing code.
+
+[note For better compile times make sure that `import std;` is available when building the `boost.type_index` module (in CMake logs there should be
+      a 'Using `import std;`' message). ]
+
+If not using CMake, then the module could be build manually from the `modules/boost_type_index.cppm` file.
+
+For manual module build the following commands can be used for clang compiler:
+
+```
+cd type_index/modules
+clang++ -I ../include -std=c++20 --precompile -x c++-module boost_type_index.cppm
+```
+
+After that, the module could be used in the following way:
+
+```
+clang++ -std=c++20 -fmodule-file=boost_type_index.pcm boost_type_index.pcm usage_sample.cpp
+```
+
+[endsect]
+
 
 [section Space and Performance]
 
diff --git a/include/boost/type_index.hpp b/include/boost/type_index.hpp
index f9a5e1c..f51854a 100644
--- a/include/boost/type_index.hpp
+++ b/include/boost/type_index.hpp
@@ -14,7 +14,7 @@
 /// By inclusion of this file most optimal type index classes will be included and used 
 /// as a boost::typeindex::type_index and boost::typeindex::type_info.
 
-#include <boost/config.hpp>
+#include <boost/type_index/detail/config.hpp>
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
@@ -49,8 +49,12 @@
 #define BOOST_TYPE_INDEX_REGISTER_CLASS
 #endif
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 #if defined(BOOST_TYPE_INDEX_DOXYGEN_INVOKED)
 
 /// \def BOOST_TYPE_INDEX_FUNCTION_SIGNATURE
@@ -257,9 +261,11 @@ inline type_index type_id_runtime(const T& runtime_val) noexcept {
     return type_index::type_id_runtime(runtime_val);
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
-
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 
 #endif // BOOST_TYPE_INDEX_HPP
 
diff --git a/include/boost/type_index/ctti_type_index.hpp b/include/boost/type_index/ctti_type_index.hpp
index fac0a3c..d680594 100644
--- a/include/boost/type_index/ctti_type_index.hpp
+++ b/include/boost/type_index/ctti_type_index.hpp
@@ -18,12 +18,19 @@
 /// It is used in situations when typeid() method is not available or 
 /// BOOST_TYPE_INDEX_FORCE_NO_RTTI_COMPATIBILITY macro is defined.
 
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #include <boost/type_index/type_index_facade.hpp>
 #include <boost/type_index/detail/compile_time_type_info.hpp>
 
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <cstring>
 #include <type_traits>
+
 #include <boost/container_hash/hash.hpp>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
@@ -64,6 +71,8 @@ public:
 
 } // namespace detail
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// Helper method for getting detail::ctti_data of a template parameter T.
 template <class T>
 inline const detail::ctti_data& ctti_construct() noexcept {
@@ -132,6 +141,8 @@ public:
     inline static ctti_type_index type_id_runtime(const T& variable) noexcept;
 };
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 
 inline const ctti_type_index::type_info_t& ctti_type_index::type_info() const noexcept {
     return *reinterpret_cast<const detail::ctti_data*>(data_);
@@ -197,8 +208,9 @@ inline std::size_t ctti_type_index::hash_code() const noexcept {
     return boost::hash_range(raw_name(), raw_name() + get_raw_name_length());
 }
 
-
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_CTTI_TYPE_INDEX_HPP
 
diff --git a/include/boost/type_index/detail/compile_time_type_info.hpp b/include/boost/type_index/detail/compile_time_type_info.hpp
index 95469bd..49f2ebe 100644
--- a/include/boost/type_index/detail/compile_time_type_info.hpp
+++ b/include/boost/type_index/detail/compile_time_type_info.hpp
@@ -13,10 +13,12 @@
 /// \brief Contains helper macros and implementation details of boost::typeindex::ctti_type_index.
 /// Not intended for inclusion from user's code.
 
-#include <boost/config.hpp>
+#include <boost/type_index/detail/config.hpp>
 
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <cstring>
 #include <type_traits>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
diff --git a/include/boost/type_index/detail/config.hpp b/include/boost/type_index/detail/config.hpp
new file mode 100644
index 0000000..041d596
--- /dev/null
+++ b/include/boost/type_index/detail/config.hpp
@@ -0,0 +1,32 @@
+//
+// Copyright 2013-2025 Antony Polukhin.
+//
+//
+// 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)
+//
+
+#ifndef BOOST_TYPE_INDEX_DETAIL_CONFIG_HPP
+#define BOOST_TYPE_INDEX_DETAIL_CONFIG_HPP
+
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+#include <boost/config.hpp>
+#ifdef BOOST_HAS_PRAGMA_ONCE
+# pragma once
+#endif
+#endif
+
+#ifdef BOOST_TYPE_INDEX_INTERFACE_UNIT
+#   define BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT export {
+#   define BOOST_TYPE_INDEX_END_MODULE_EXPORT }
+#else
+#   define BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+#   define BOOST_TYPE_INDEX_END_MODULE_EXPORT
+#endif
+
+#if defined(BOOST_USE_MODULES) && !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+import boost.type_index;
+#endif
+
+#endif // BOOST_TYPE_INDEX_DETAIL_CONFIG_HPP
+
diff --git a/include/boost/type_index/detail/ctti_register_class.hpp b/include/boost/type_index/detail/ctti_register_class.hpp
index e004be0..b8dd905 100644
--- a/include/boost/type_index/detail/ctti_register_class.hpp
+++ b/include/boost/type_index/detail/ctti_register_class.hpp
@@ -19,15 +19,23 @@
 # pragma once
 #endif
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 namespace boost { namespace typeindex { namespace detail {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 template <class T>
 inline const ctti_data& ctti_construct_typeid_ref(const T*) noexcept {
     return boost::typeindex::ctti_construct<T>();
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }}} // namespace boost::typeindex::detail
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 /// @cond
 #define BOOST_TYPE_INDEX_REGISTER_CLASS                                                                       \
     virtual const boost::typeindex::detail::ctti_data& boost_type_index_type_id_runtime_() const noexcept {   \
diff --git a/include/boost/type_index/detail/stl_register_class.hpp b/include/boost/type_index/detail/stl_register_class.hpp
index 0e44a26..67b34f3 100644
--- a/include/boost/type_index/detail/stl_register_class.hpp
+++ b/include/boost/type_index/detail/stl_register_class.hpp
@@ -19,15 +19,23 @@
 # pragma once
 #endif
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 namespace boost { namespace typeindex { namespace detail {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 template <class T>
 inline const stl_type_index::type_info_t& stl_construct_typeid_ref(const T*) noexcept {
     return typeid(T);
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }}} // namespace boost::typeindex::detail
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 /// @cond
 #define BOOST_TYPE_INDEX_REGISTER_CLASS                                                                               \
     virtual const boost::typeindex::stl_type_index::type_info_t& boost_type_index_type_id_runtime_() const noexcept { \
diff --git a/include/boost/type_index/runtime_cast.hpp b/include/boost/type_index/runtime_cast.hpp
index c72b119..d1adccf 100644
--- a/include/boost/type_index/runtime_cast.hpp
+++ b/include/boost/type_index/runtime_cast.hpp
@@ -9,6 +9,8 @@
 #ifndef BOOST_TYPE_INDEX_RUNTIME_CAST_HPP
 #define BOOST_TYPE_INDEX_RUNTIME_CAST_HPP
 
+#include <boost/type_index/detail/config.hpp>
+
 /// \file runtime_cast.hpp
 /// \brief Contains the basic utilities necessary to fully emulate
 /// dynamic_cast for language level constructs (raw pointers and references).
diff --git a/include/boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp b/include/boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp
index 2664c01..a1af74e 100644
--- a/include/boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp
+++ b/include/boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp
@@ -13,21 +13,25 @@
 /// \brief Contains the overload of boost::typeindex::runtime_pointer_cast for
 /// boost::shared_ptr types.
 
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #include <boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp>
 
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <type_traits>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
-namespace boost {
-    template<class T> class shared_ptr;
-}
-
 namespace boost { namespace typeindex {
 
-/// \brief Creates a new instance of std::shared_ptr whose stored pointer is obtained from u's
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
+/// \brief Creates a new instance of smart pointer whose stored pointer is obtained from u's
 /// stored pointer using a runtime_cast.
 ///
 /// The new shared_ptr will share ownership with u, except that it is empty if the runtime_cast
@@ -37,14 +41,18 @@ namespace boost { namespace typeindex {
 /// \return If there exists a valid conversion from U* to T*, returns a boost::shared_ptr<T>
 /// that points to an address suitably offset from u.
 /// If no such conversion exists, returns boost::shared_ptr<T>();
-template<typename T, typename U>
-boost::shared_ptr<T> runtime_pointer_cast(boost::shared_ptr<U> const& u) {
+template<typename T, typename U,  template <class> class SmartPointer>
+auto runtime_pointer_cast(SmartPointer<U> const& u) -> decltype(u.use_count(), SmartPointer<T>()) {
     T* value = detail::runtime_cast_impl<T>(u.get(), std::is_base_of<T, U>());
     if(value)
-        return boost::shared_ptr<T>(u, value);
-    return boost::shared_ptr<T>();
+        return SmartPointer<T>(u, value);
+    return SmartPointer<T>();
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_RUNTIME_CAST_BOOST_SHARED_PTR_CAST_HPP
diff --git a/include/boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp b/include/boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp
index 12a1b0e..8b6ed5f 100644
--- a/include/boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp
+++ b/include/boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp
@@ -19,7 +19,9 @@
 
 #include <boost/type_index.hpp>
 
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <type_traits>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
diff --git a/include/boost/type_index/runtime_cast/pointer_cast.hpp b/include/boost/type_index/runtime_cast/pointer_cast.hpp
index e4f94c1..f30a6d5 100644
--- a/include/boost/type_index/runtime_cast/pointer_cast.hpp
+++ b/include/boost/type_index/runtime_cast/pointer_cast.hpp
@@ -12,16 +12,22 @@
 /// \file pointer_class.hpp
 /// \brief Contains the function overloads of boost::typeindex::runtime_cast for
 /// pointer types.
+
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #include <boost/type_index.hpp>
 #include <boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp>
 
-
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// \brief Safely converts pointers to classes up, down, and sideways along the inheritance hierarchy.
 /// \tparam T The desired target type. Like dynamic_cast, must be a pointer to complete class type.
 /// \tparam U A complete class type of the source instance, u.
@@ -68,6 +74,10 @@ T const* runtime_pointer_cast(U const* u) noexcept {
     return detail::runtime_cast_impl<T>(u, std::is_base_of<T, U>());
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_RUNTIME_CAST_POINTER_CAST_HPP
diff --git a/include/boost/type_index/runtime_cast/reference_cast.hpp b/include/boost/type_index/runtime_cast/reference_cast.hpp
index 674a289..08f997c 100644
--- a/include/boost/type_index/runtime_cast/reference_cast.hpp
+++ b/include/boost/type_index/runtime_cast/reference_cast.hpp
@@ -13,18 +13,27 @@
 /// \brief Contains the overload of boost::typeindex::runtime_cast for
 /// reference types.
 
-#include <boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp>
-#include <boost/throw_exception.hpp>
+#include <boost/type_index/detail/config.hpp>
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
+#include <boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp>
+
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <memory>
 #include <type_traits>
 
+#include <boost/throw_exception.hpp>
+#endif
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// \brief Indicates that runtime_cast was unable to perform the desired cast operation
 /// because the source instance was not also an instance of the target type.
 struct BOOST_SYMBOL_VISIBLE bad_runtime_cast : std::exception
@@ -60,6 +69,10 @@ typename std::add_lvalue_reference<const T>::type runtime_cast(U const& u) {
     return *value;
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_RUNTIME_CAST_REFERENCE_CAST_HPP
diff --git a/include/boost/type_index/runtime_cast/register_runtime_class.hpp b/include/boost/type_index/runtime_cast/register_runtime_class.hpp
index 957224e..db45285 100644
--- a/include/boost/type_index/runtime_cast/register_runtime_class.hpp
+++ b/include/boost/type_index/runtime_cast/register_runtime_class.hpp
@@ -12,14 +12,21 @@
 /// \file register_runtime_class.hpp
 /// \brief Contains the macros BOOST_TYPE_INDEX_IMPLEMENT_RUNTIME_CAST and
 /// BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS
+
+#include <boost/type_index/detail/config.hpp>
+
 #include <boost/type_index.hpp>
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
 namespace boost { namespace typeindex { namespace detail {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 template<typename T>
 inline type_index runtime_class_construct_type_id(T const*) {
     return boost::typeindex::type_id<T>();
@@ -39,8 +46,12 @@ const void* find_instance(boost::typeindex::type_index const& idx, const Self* s
     return boost::typeindex::detail::find_instance<OtherBases...>(idx, self);
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }}} // namespace boost::typeindex::detail
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 
 /// \def BOOST_TYPE_INDEX_REGISTER_RUNTIME_CLASS
 /// \brief Macro used to make a class compatible with boost::typeindex::runtime_cast
diff --git a/include/boost/type_index/runtime_cast/std_shared_ptr_cast.hpp b/include/boost/type_index/runtime_cast/std_shared_ptr_cast.hpp
index 7b09db5..8fcdc17 100644
--- a/include/boost/type_index/runtime_cast/std_shared_ptr_cast.hpp
+++ b/include/boost/type_index/runtime_cast/std_shared_ptr_cast.hpp
@@ -13,8 +13,15 @@
 /// \brief Contains the overload of boost::typeindex::runtime_pointer_cast for
 /// std::shared_ptr types.
 
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #include <boost/type_index/runtime_cast/detail/runtime_cast_impl.hpp>
+
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <memory>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
@@ -22,6 +29,8 @@
 
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// \brief Creates a new instance of std::shared_ptr whose stored pointer is obtained from u's
 /// stored pointer using a runtime_cast.
 ///
@@ -40,6 +49,10 @@ std::shared_ptr<T> runtime_pointer_cast(std::shared_ptr<U> const& u) {
     return std::shared_ptr<T>();
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_RUNTIME_CAST_STD_SHARED_PTR_CAST_HPP
diff --git a/include/boost/type_index/stl_type_index.hpp b/include/boost/type_index/stl_type_index.hpp
index 680ef9a..810339a 100644
--- a/include/boost/type_index/stl_type_index.hpp
+++ b/include/boost/type_index/stl_type_index.hpp
@@ -19,6 +19,10 @@
 /// When typeid() is disabled or BOOST_TYPE_INDEX_FORCE_NO_RTTI_COMPATIBILITY macro
 /// is defined boost::typeindex::ctti is usually used instead of boost::typeindex::stl_type_index.
 
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #include <boost/type_index/type_index_facade.hpp>
 
 // MSVC is capable of calling typeid(T) even when RTTI is off
@@ -26,12 +30,15 @@
 #error "File boost/type_index/stl_type_index.ipp is not usable when typeid() is not available."
 #endif
 
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <typeinfo>
 #include <cstring>                                  // std::strcmp, std::strlen, std::strstr
 #include <stdexcept>
 #include <type_traits>
+
 #include <boost/throw_exception.hpp>
 #include <boost/core/demangle.hpp>
+#endif
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
@@ -39,6 +46,8 @@
 
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// \class stl_type_index
 /// This class is a wrapper around std::type_info, that workarounds issues and provides
 /// much more rich interface. \b For \b description \b of \b functions \b see type_index_facade.
@@ -93,6 +102,8 @@ public:
     inline static stl_type_index type_id_runtime(const T& value) noexcept;
 };
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 inline const stl_type_index::type_info_t& stl_type_index::type_info() const noexcept {
     return *data_;
 }
@@ -111,7 +122,7 @@ inline const char* stl_type_index::name() const noexcept {
 }
 
 inline std::string stl_type_index::pretty_name() const {
-    static const char cvr_saver_name[] = "boost::typeindex::detail::cvr_saver<";
+    static const char cvr_saver_name[] = "boost::typeindex::detail::cvr_saver";
     static BOOST_CONSTEXPR_OR_CONST std::string::size_type cvr_saver_name_len = sizeof(cvr_saver_name) - 1;
 
     // In case of MSVC demangle() is a no-op, and name() already returns demangled name.
@@ -131,6 +142,12 @@ inline std::string stl_type_index::pretty_name() const {
         if (b) {
             b += cvr_saver_name_len;
 
+            // Trim everuthing till '<'. In modules the name could be boost::typeindex::detail::cvr_saver@boost.type_index<
+            while (*b != '<') {         // the string is zero terminated, we won't exceed the buffer size
+                ++ b;
+            }
+            ++b;
+
             // Trim leading spaces
             while (*b == ' ') {         // the string is zero terminated, we won't exceed the buffer size
                 ++ b;
@@ -231,4 +248,6 @@ inline stl_type_index stl_type_index::type_id_runtime(const T& value) noexcept {
 
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_STL_TYPE_INDEX_HPP
diff --git a/include/boost/type_index/type_index_facade.hpp b/include/boost/type_index/type_index_facade.hpp
index 891797e..7e6261e 100644
--- a/include/boost/type_index/type_index_facade.hpp
+++ b/include/boost/type_index/type_index_facade.hpp
@@ -9,19 +9,28 @@
 #ifndef BOOST_TYPE_INDEX_TYPE_INDEX_FACADE_HPP
 #define BOOST_TYPE_INDEX_TYPE_INDEX_FACADE_HPP
 
-#include <boost/config.hpp>
-#include <boost/container_hash/hash_fwd.hpp>
+#include <boost/type_index/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
+#if !defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
 #include <string>
 #include <cstring>
 #include <type_traits>
 #include <iosfwd>               // for std::basic_ostream
 
+#include <boost/config.hpp>
+#include <boost/container_hash/hash_fwd.hpp>
+#endif
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
 namespace boost { namespace typeindex {
 
+BOOST_TYPE_INDEX_BEGIN_MODULE_EXPORT
+
 /// \class type_index_facade
 ///
 /// This class takes care about the comparison operators, hash functions and 
@@ -274,7 +283,11 @@ inline std::size_t hash_value(const type_index_facade<Derived, TypeInfo>& lhs) n
     return static_cast<Derived const&>(lhs).hash_code();
 }
 
+BOOST_TYPE_INDEX_END_MODULE_EXPORT
+
 }} // namespace boost::typeindex
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_TYPE_INDEX_INTERFACE_UNIT)
+
 #endif // BOOST_TYPE_INDEX_TYPE_INDEX_FACADE_HPP
 
diff --git a/modules/boost_type_index.cppm b/modules/boost_type_index.cppm
new file mode 100644
index 0000000..37061c1
--- /dev/null
+++ b/modules/boost_type_index.cppm
@@ -0,0 +1,55 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// 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)
+
+// To compile manually use a command like the folowing:
+// clang++ -I ../include -std=c++20 --precompile -x c++-module pfr.cppm
+
+module;
+
+#include <version>
+#include <cstddef>
+#include <cstdint>
+
+#include <boost/config.hpp>
+#include <boost/container_hash/hash_fwd.hpp>
+#include <boost/container_hash/hash.hpp>
+#include <boost/core/demangle.hpp>
+#include <boost/throw_exception.hpp>
+
+#ifndef BOOST_TYPE_INDEX_USE_STD_MODULE
+#include <cstring>
+#include <iosfwd>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <typeinfo>
+#include <type_traits>
+#endif
+
+#define BOOST_TYPE_INDEX_INTERFACE_UNIT
+
+export module boost.type_index;
+
+#ifdef BOOST_TYPE_INDEX_USE_STD_MODULE
+// Should not be in the global module fragment
+// https://eel.is/c++draft/module#global.frag-1
+import std;
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
+#endif
+
+#include <boost/type_index.hpp>
+#include <boost/type_index/ctti_type_index.hpp>
+#include <boost/type_index/runtime_cast.hpp>
+#include <boost/type_index/runtime_cast/boost_shared_ptr_cast.hpp>
+#include <boost/type_index/runtime_cast/pointer_cast.hpp>
+#include <boost/type_index/runtime_cast/reference_cast.hpp>
+#include <boost/type_index/runtime_cast/register_runtime_class.hpp>
+#include <boost/type_index/runtime_cast/std_shared_ptr_cast.hpp>
+#include <boost/type_index/stl_type_index.hpp>
+#include <boost/type_index/type_index_facade.hpp>
+
diff --git a/modules/usage_sample.cpp b/modules/usage_sample.cpp
new file mode 100644
index 0000000..89b82b2
--- /dev/null
+++ b/modules/usage_sample.cpp
@@ -0,0 +1,18 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// 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)
+
+// To compile manually use a command like the folowing:
+// clang++ -std=c++20 -fmodule-file=type_index.pcm type_index.pcm usage_sample.cpp
+
+//[type_index_module_example
+#include <iostream>
+
+import boost.type_index;
+
+int main() {
+    std::cout << boost::typeindex::type_id_with_cvr<const int>();  // Outputs: const int
+}
+//]
+
diff --git a/modules/usage_test_mu1.cpp b/modules/usage_test_mu1.cpp
new file mode 100644
index 0000000..001145d
--- /dev/null
+++ b/modules/usage_test_mu1.cpp
@@ -0,0 +1,13 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// 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)
+
+#include <iostream>
+
+import boost.type_index;
+
+void do_something(std::ostream& os) {
+    os << boost::typeindex::type_id_with_cvr<const int>();
+}
+
diff --git a/modules/usage_test_mu2.cpp b/modules/usage_test_mu2.cpp
new file mode 100644
index 0000000..120539c
--- /dev/null
+++ b/modules/usage_test_mu2.cpp
@@ -0,0 +1,16 @@
+// Copyright (c) 2016-2025 Antony Polukhin
+//
+// 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)
+
+#include <iostream>
+#include <boost/type_index.hpp>
+
+void do_something(std::ostream& os);
+
+int main() {
+    do_something(std::cout);
+    std::cout << '\n';
+    std::cout << boost::typeindex::type_id_with_cvr<const int>();  // Outputs: const int
+}
+
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 90ab669..fb91641 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -50,10 +50,10 @@ exe testing_crossmodule_anonymous_no_rtti : testing_crossmodule_anonymous.cpp te
 
 test-suite type_index
   :
-    [ run type_index_test.cpp /boost/lexical_cast//boost_lexical_cast ]
+    [ run type_index_test.cpp ]
     [ run type_index_runtime_cast_test.cpp /boost/smart_ptr//boost_smart_ptr ]
     [ run type_index_constexpr_test.cpp ]
-    [ run type_index_test.cpp /boost/lexical_cast//boost_lexical_cast : : : <rtti>off $(norttidefines) : type_index_test_no_rtti ]
+    [ run type_index_test.cpp : : : <rtti>off $(norttidefines) : type_index_test_no_rtti ]
     [ run ctti_print_name.cpp : : : <test-info>always_show_run_output ]
     [ run testing_crossmodule.cpp test_lib_rtti ]
     [ run testing_crossmodule.cpp test_lib_nortti : : : <rtti>off $(norttidefines) : testing_crossmodule_no_rtti ]
diff --git a/test/cmake_subdir_test/CMakeLists.txt b/test/cmake_subdir_test/CMakeLists.txt
new file mode 100644
index 0000000..645507b
--- /dev/null
+++ b/test/cmake_subdir_test/CMakeLists.txt
@@ -0,0 +1,52 @@
+# Copyright  (c) 2016-2025 Antony Polukhin
+# 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
+
+cmake_minimum_required(VERSION 3.5...4.0)
+
+project(type_index_subdir_test LANGUAGES CXX)
+
+add_subdirectory(../../../assert boostorg/assert)
+add_subdirectory(../../../core boostorg/core)
+add_subdirectory(../../../config boostorg/config)
+add_subdirectory(../../../container_hash boostorg/container_hash)
+add_subdirectory(../../../describe boostorg/describe)
+add_subdirectory(../../../detail boostorg/detail)
+add_subdirectory(../../../integer boostorg/integer)
+add_subdirectory(../../../move boostorg/move)
+add_subdirectory(../../../mp11 boostorg/mp11)
+add_subdirectory(../../../preprocessor boostorg/preprocessor)
+add_subdirectory(../../../smart_ptr boostorg/smart_ptr)
+add_subdirectory(../../../static_assert boostorg/static_assert)
+add_subdirectory(../../../throw_exception boostorg/throw_exception)
+add_subdirectory(../../../type_traits boostorg/type_traits)
+
+add_subdirectory(../../ boostorg/type_index)
+
+enable_testing()
+
+if (BOOST_USE_MODULES)
+    add_executable(boost_type_index_module_usage ../../modules/usage_sample.cpp)
+    target_link_libraries(boost_type_index_module_usage PRIVATE Boost::type_index)
+    add_test(NAME boost_type_index_module_usage COMMAND boost_type_index_module_usage)
+
+    # Make sure that mixing includes and imports is fine for different TU
+    add_executable(boost_type_index_module_usage_mu ../../modules/usage_test_mu1.cpp ../../modules/usage_test_mu2.cpp)
+    target_link_libraries(boost_type_index_module_usage_mu PRIVATE Boost::type_index)
+    add_test(NAME boost_type_index_module_usage_mu COMMAND boost_type_index_module_usage_mu)
+endif()
+
+list(APPEND RUN_TESTS_SOURCES
+    compare_ctti_stl.cpp
+    ctti_print_name.cpp
+    track_13621.cpp
+    type_index_runtime_cast_test.cpp
+    type_index_test.cpp
+)
+
+foreach (testsourcefile ${RUN_TESTS_SOURCES})
+    get_filename_component(testname ${testsourcefile} NAME_WLE)
+    add_executable(${PROJECT_NAME}_${testname} ../${testsourcefile})
+    target_link_libraries(${PROJECT_NAME}_${testname} Boost::type_index Boost::smart_ptr)
+    add_test(NAME ${PROJECT_NAME}_${testname} COMMAND ${PROJECT_NAME}_${testname})
+endforeach()
diff --git a/test/compare_ctti_stl.cpp b/test/compare_ctti_stl.cpp
index fdcbfd1..b8c0c34 100644
--- a/test/compare_ctti_stl.cpp
+++ b/test/compare_ctti_stl.cpp
@@ -34,8 +34,8 @@ void compare()
     typedef boost::typeindex::ctti_type_index ctti;
     typedef boost::typeindex::stl_type_index stl;
     BOOST_TEST_EQ(
-        ctti::type_id<int>().pretty_name(),
-        stl::type_id<int>().pretty_name()
+        ctti::type_id<T>().pretty_name(),
+        stl::type_id<T>().pretty_name()
     );
 }
 
@@ -44,14 +44,15 @@ int main()
 {
     compare<void>();
     compare<int>();
-    compare<double*>();
     compare<const double&>();
+
+#ifndef _MSC_VER  // may add `class` to the type name
     compare<my_namespace1::my_class>();
 
     compare<my_namespace3::my_template<
             my_namespace1::my_class,
             my_namespace2::my_class> >();
-
+#endif
 
     return boost::report_errors();
 }
diff --git a/test/type_index_test.cpp b/test/type_index_test.cpp
index ccb391e..99286b2 100644
--- a/test/type_index_test.cpp
+++ b/test/type_index_test.cpp
@@ -7,7 +7,7 @@
 
 #include <boost/type_index.hpp>
 
-#include <boost/lexical_cast.hpp>
+#include <sstream>
 
 #include <boost/core/lightweight_test.hpp>
 
@@ -209,15 +209,20 @@ void type_id_storing_modifiers_vs_nonstoring()
     BOOST_TEST(t1.pretty_name() == "const int" || t1.pretty_name() == "int const");
 }
 
-void type_index_stream_operator_via_lexical_cast_testing()
+void type_index_stream_operator_via_stringstream_testing()
 {
     using namespace boost::typeindex;
 
-    std::string s_int2 = boost::lexical_cast<std::string>(type_id<int>());
-    BOOST_TEST_EQ(s_int2, "int");
-
-    std::string s_double2 = boost::lexical_cast<std::string>(type_id<double>());
-    BOOST_TEST_EQ(s_double2, "double");
+    {
+        std::ostringstream oss;
+        oss << type_id<int>();
+        BOOST_TEST_EQ(oss.str(), "int");
+    }
+    {
+        std::ostringstream oss;
+        oss << type_id<double>();
+        BOOST_TEST_EQ(oss.str(), "double");
+    }
 }
 
 void type_index_stripping_cvr_test()
@@ -386,7 +391,7 @@ int main() {
 
     type_id_storing_modifiers();
     type_id_storing_modifiers_vs_nonstoring();
-    type_index_stream_operator_via_lexical_cast_testing();
+    type_index_stream_operator_via_stringstream_testing();
     type_index_stripping_cvr_test();
     type_index_user_defined_class_test();