Initial support for C++20 modules (#177)

CMakeLists.txt

@@ -1,5 +1,6 @@
-# Generated by `boostdep --cmake pfr`
 # Copyright 2020 Peter Dimov
+# Copyright (c) 2016-2024 Antony Polukhin
+#
 # Distributed under the Boost Software License, Version 1.0.
 # https://www.boost.org/LICENSE_1_0.txt
 
@@ -12,9 +13,11 @@ add_library(Boost::pfr ALIAS boost_pfr)
 
 target_include_directories(boost_pfr INTERFACE include)
 
-if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
-
-  add_subdirectory(test)
-
+if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.28.0" AND BUILD_MODULE)
+    add_subdirectory(module)
+endif()
+
+if (BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
+  add_subdirectory(test)
 endif()
 

doc/pfr.qbk

@@ -549,6 +549,40 @@ parameters provided to `BOOST_PFR_CORE_NAME_PARSING` macro [*and] the initial ou
 
 [endsect]
 
+[section PFR as a C++20 module]
+
+[caution C++20 PFR module support is on early stage, targets and flags may change in the future]
+
+If using CMake of version 3.28.0 or higher define CMake option `-DBUILD_MODULE=1`
+to make the `Boost::pfr_module` and `Boost::pfr_module_migration` libraries
+available. With `Boost::pfr_module` C++20 module Boost.PFR could be used:
+
+[import ../module/usage_sample.cpp]
+[pfr_module_example]
+
+The `Boost::pfr_module_migration` CMake target gives an ability to
+mix includes and imports of the PFR library in different translation units.
+
+If not using CMake, then the module could be build manually from the
+`module/pfr.cppm` file. If mixing of includes in imports is desired, additionally
+define `BOOST_PFR_ATTACH_TO_GLOBAL_MODULE` preprocessor macro to attach all the
+module entities to a global module and avoid ODR issues.
+
+For manual module build the following commands could be used for clang compiler:
+
+```
+cd pfr/module
+clang++ -I ../include -std=c++20 --precompile -x c++-module pfr.cppm
+```
+
+After that, the module could be used in the following way:
+
+```
+clang++ -std=c++20 -fmodule-file=pfr.pcm pfr.pcm usage_sample.cpp
+```
+
+[endsect]
+
 [section How it works]
 
 [h2 Fields count detection and getting references to members]

include/boost/pfr/config.hpp

@@ -145,4 +145,12 @@
 
 #undef BOOST_PFR_NOT_SUPPORTED
 
+#ifndef BOOST_PFR_BEGIN_MODULE_EXPORT
+#   define BOOST_PFR_BEGIN_MODULE_EXPORT
+#endif
+
+#ifndef BOOST_PFR_END_MODULE_EXPORT
+#   define BOOST_PFR_END_MODULE_EXPORT
+#endif
+
 #endif // BOOST_PFR_CONFIG_HPP

include/boost/pfr/core.hpp

@@ -29,6 +29,8 @@
 
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// \brief Returns reference or const reference to a field with index `I` in \aggregate `val`.
 /// Overload taking the type `U` returns reference or const reference to a field
 /// with provided type `U` in \aggregate `val` if there's only one field of such type in `val`.
@@ -260,6 +262,8 @@ constexpr detail::tie_from_structure_tuple<Elements...> tie_from_structure(Eleme
     return detail::tie_from_structure_tuple<Elements...>(args...);
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_CORE_HPP

include/boost/pfr/core_name.hpp

@@ -33,6 +33,8 @@
 
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// \brief Returns name of a field with index `I` in \aggregate `T`.
 ///
 /// \b Example:
@@ -82,6 +84,8 @@ names_as_array() noexcept {
     );
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_CORE_NAME_HPP

include/boost/pfr/detail/core14_classic.hpp

@@ -9,8 +9,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <utility>      // metaprogramming stuff
+#endif
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/offset_based_getter.hpp>

include/boost/pfr/detail/core14_loophole.hpp

@@ -24,8 +24,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <utility>
+#endif
 
 #include <boost/pfr/detail/offset_based_getter.hpp>
 #include <boost/pfr/detail/fields_count.hpp>

include/boost/pfr/detail/core17_generated.hpp

@@ -21,7 +21,12 @@
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/size_t_.hpp>
+
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits> // for std::conditional_t, std::is_reference
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/core_name20_static.hpp

@@ -19,10 +19,15 @@
 #include <boost/pfr/detail/fields_count.hpp>
 #include <boost/pfr/detail/stdarray.hpp>
 #include <boost/pfr/detail/fake_object.hpp>
+
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <string_view>
 #include <array>
 #include <memory> // for std::addressof
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/detectors.hpp

@@ -9,8 +9,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <functional>
 #include <type_traits>
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 ///////////////////// `value` is true if Detector<Tleft, Tright> does not compile (SFINAE)

include/boost/pfr/detail/fields_count.hpp

@@ -12,9 +12,13 @@
 #include <boost/pfr/detail/size_t_.hpp>
 #include <boost/pfr/detail/unsafe_declval.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <climits>      // CHAR_BIT
 #include <type_traits>
 #include <utility>      // metaprogramming stuff
+#endif
 
 #ifdef __clang__
 #   pragma clang diagnostic push

include/boost/pfr/detail/for_each_field_impl.hpp

@@ -9,7 +9,11 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <utility>      // metaprogramming stuff
+#endif
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/rvalue_t.hpp>

include/boost/pfr/detail/functional.hpp

@@ -9,8 +9,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <functional>
 #include <cstdint>
+#endif
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 

include/boost/pfr/detail/io.hpp

@@ -10,6 +10,10 @@
 #include <boost/pfr/detail/config.hpp>
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
+
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <iosfwd>       // stream operators
 #include <iomanip>
 
@@ -19,6 +23,8 @@
 #   endif
 #endif
 
+#endif
+
 namespace boost { namespace pfr { namespace detail {
 
 inline auto quoted_helper(const std::string& s) noexcept {

include/boost/pfr/detail/make_flat_tuple_of_references.hpp

@@ -9,7 +9,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <utility>      // metaprogramming stuff
+#endif
+
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/rvalue_t.hpp>
 #include <boost/pfr/detail/make_integer_sequence.hpp>

include/boost/pfr/detail/make_integer_sequence.hpp

@@ -10,9 +10,13 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <utility>
 #include <cstddef>
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/offset_based_getter.hpp

@@ -10,9 +10,14 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <utility>
 #include <memory>  // std::addressof
+#endif
+
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/rvalue_t.hpp>
 #include <boost/pfr/detail/size_t_.hpp>

include/boost/pfr/detail/possible_reflectable.hpp

@@ -10,7 +10,11 @@
 #include <boost/pfr/detail/config.hpp>
 #include <boost/pfr/traits_fwd.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits> // for std::is_aggregate
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/rvalue_t.hpp

@@ -7,8 +7,12 @@
 #define BOOST_PFR_DETAIL_RVALUE_T_HPP
 #pragma once
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
 #include <utility>      // std::enable_if_t
+#endif
 
 // This header provides aliases rvalue_t and lvalue_t.
 //

include/boost/pfr/detail/sequence_tuple.hpp

@@ -10,8 +10,12 @@
 #include <boost/pfr/detail/config.hpp>
 #include <boost/pfr/detail/make_integer_sequence.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <utility>      // metaprogramming stuff
 #include <cstddef>      // std::size_t
+#endif
 
 ///////////////////// Tuple that holds its values in the supplied order
 namespace boost { namespace pfr { namespace detail { namespace sequence_tuple {

include/boost/pfr/detail/size_array.hpp

@@ -9,7 +9,11 @@
 
 #include <boost/pfr/detail/config.hpp>
 
-#include <cstddef>      // metaprogramming stuff
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
+#include <cstddef>
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/stdarray.hpp

@@ -9,10 +9,14 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <utility> // metaprogramming stuff
 #include <array>
 #include <type_traits> // for std::common_type_t
 #include <cstddef>
+#endif
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 

include/boost/pfr/detail/stdtuple.hpp

@@ -9,8 +9,12 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <utility>      // metaprogramming stuff
 #include <tuple>
+#endif
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 

include/boost/pfr/detail/tie_from_structure_tuple.hpp

@@ -16,7 +16,11 @@
 #include <boost/pfr/tuple_size.hpp>
 #include <boost/pfr/detail/make_integer_sequence.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <tuple>
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/detail/unsafe_declval.hpp

@@ -9,7 +9,11 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits>
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

include/boost/pfr/functors.hpp

@@ -35,6 +35,8 @@
 /// \b Synopsis:
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 ///////////////////// Comparisons
 
 /// \brief std::equal_to like comparator that returns \forcedlink{eq}(x, y)
@@ -216,6 +218,8 @@ template <class T> struct hash {
     }
 };
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_FUNCTORS_HPP

include/boost/pfr/io.hpp

@@ -67,6 +67,8 @@ struct io_impl {
     T value;
 };
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 template <class Char, class Traits, class T>
 enable_not_ostreamable_t<std::basic_ostream<Char, Traits>, T> operator<<(std::basic_ostream<Char, Traits>& out, io_impl<T>&& x) {
     return out << boost::pfr::io_fields(std::forward<T>(x.value));
@@ -87,8 +89,12 @@ enable_istreamable_t<std::basic_istream<Char, Traits>, T> operator>>(std::basic_
     return in >> x.value;
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 } // namespace detail
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// IO manipulator to read/write \aggregate `value` using its IO stream operators or using \forcedlink{io_fields} if operators are not available.
 ///
 /// \b Example:
@@ -108,6 +114,8 @@ auto io(T&& value) noexcept {
     return detail::io_impl<T>{std::forward<T>(value)};
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_IO_HPP

include/boost/pfr/io_fields.hpp

@@ -118,6 +118,8 @@ std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char, Traits>& i
     return in;
 }
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 template <class Char, class Traits, class T>
 std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char, Traits>& in, io_fields_impl<const T&>&& ) {
     static_assert(sizeof(T) && false, "====================> Boost.PFR: Attempt to use istream operator on a boost::pfr::io_fields wrapped type T with const qualifier.");
@@ -130,8 +132,12 @@ std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char, Traits>& i
     return in;
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 } // namespace detail
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// IO manipulator to read/write \aggregate `value` field-by-field.
 ///
 /// \b Example:
@@ -159,6 +165,8 @@ auto io_fields(T&& value) noexcept {
     return detail::io_fields_impl<T>{std::forward<T>(value)};
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_IO_FIELDS_HPP

include/boost/pfr/ops.hpp

@@ -77,6 +77,7 @@ namespace detail {
     >;
 } // namespace detail
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
 
 /// \brief Compares lhs and rhs for equality using their own comparison and conversion operators; if no operators available returns \forcedlink{eq_fields}(lhs, rhs).
 ///
@@ -182,6 +183,8 @@ constexpr detail::enable_hashable_t<T> hash_value(const T& value) {
     return std::hash<T>{}(value);
 }
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_OPS_HPP

include/boost/pfr/ops_fields.hpp

@@ -33,6 +33,8 @@
 /// \b Synopsis:
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
     /// Does a field-by-field equality comparison.
     ///
     /// \returns `L == R && tuple_size_v<T> == tuple_size_v<U>`, where `L` and
@@ -122,6 +124,9 @@ namespace boost { namespace pfr {
         return result;
 #endif
     }
+
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_OPS_HPP

include/boost/pfr/traits.hpp

@@ -19,6 +19,8 @@
 
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// Has a static const member variable `value` when it is known that type T can or can't be reflected using Boost.PFR; otherwise, there is no member variable.
 /// Every user may (and in some difficult cases - should) specialize is_reflectable on his own.
 ///
@@ -54,6 +56,8 @@ using is_implicitly_reflectable = std::integral_constant< bool, boost::pfr::deta
 template<class T, class WhatFor>
 constexpr bool is_implicitly_reflectable_v = is_implicitly_reflectable<T, WhatFor>::value;
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_TRAITS_HPP

include/boost/pfr/traits_fwd.hpp

@@ -11,9 +11,13 @@
 
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 template<class T, class WhatFor>
 struct is_reflectable;
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_DETAIL_TRAITS_FWD_HPP

include/boost/pfr/tuple_size.hpp

@@ -22,6 +22,8 @@
 /// \b Synopsis:
 namespace boost { namespace pfr {
 
+BOOST_PFR_BEGIN_MODULE_EXPORT
+
 /// Has a static const member variable `value` that contains fields count in a T.
 /// Works for any T that satisfies \aggregate.
 ///
@@ -43,6 +45,8 @@ using tuple_size = detail::size_t_< boost::pfr::detail::fields_count<T>() >;
 template <class T>
 constexpr std::size_t tuple_size_v = tuple_size<T>::value;
 
+BOOST_PFR_END_MODULE_EXPORT
+
 }} // namespace boost::pfr
 
 #endif // BOOST_PFR_TUPLE_SIZE_HPP

misc/generate_cpp17.py

@@ -38,7 +38,12 @@ PROLOGUE = """// Copyright (c) 2016-2024 Antony Polukhin
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/size_t_.hpp>
+
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#else
 #include <type_traits> // for std::conditional_t, std::is_reference
+#endif
 
 namespace boost { namespace pfr { namespace detail {
 

module/CMakeLists.txt

@@ -0,0 +1,37 @@
+# Copyright (c) 2016-2024 Antony Polukhin
+#
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.28)
+
+function (_add_boost_pfr_module_impl NAME)
+    add_library(${NAME})
+    target_compile_features(${NAME} PUBLIC cxx_std_20)
+    target_sources(${NAME} PUBLIC
+        FILE_SET modules_public TYPE CXX_MODULES FILES
+            ${CMAKE_CURRENT_LIST_DIR}/pfr.cppm
+    )
+endfunction()
+
+function (add_boost_pfr_module NAME)
+    _add_boost_pfr_module_impl(${NAME})
+    target_include_directories(${NAME} PRIVATE ${CMAKE_CURRENT_LIST_DIR}/../include)
+
+    _add_boost_pfr_module_impl(${NAME}_migration)
+    target_include_directories(${NAME}_migration PUBLIC ${CMAKE_CURRENT_LIST_DIR}/../include)
+    target_compile_definitions(${NAME}_migration PRIVATE BOOST_PFR_ATTACH_TO_GLOBAL_MODULE)
+endfunction()
+
+add_boost_pfr_module(boost_pfr_module)
+add_library(Boost::pfr_module ALIAS boost_pfr_module)
+add_library(Boost::pfr_module_migration ALIAS boost_pfr_module_migration)
+
+if (BUILD_TESTING)
+    add_executable(boost_pfr_module_usage usage_sample.cpp)
+    target_link_libraries(boost_pfr_module_usage PRIVATE Boost::pfr_module)
+
+    # Make sure that mixing includes and imports is fine for different TU
+    add_executable(boost_pfr_module_usage_mu usage_test_mu1.cpp usage_test_mu2.cpp)
+    target_link_libraries(boost_pfr_module_usage_mu PRIVATE Boost::pfr_module_migration)
+endif()

module/pfr.cppm

@@ -0,0 +1,44 @@
+// Copyright (c) 2016-2024 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
+
+#define BOOST_PFR_BEGIN_MODULE_EXPORT export {
+#define BOOST_PFR_END_MODULE_EXPORT }
+
+#ifndef BOOST_PFR_HAS_STD_MODULE
+module;
+#include <array>
+#include <cstddef>
+#include <functional>
+#include <iomanip>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+#include <variant>
+#endif
+
+export module Boost.PFR;
+
+#ifdef BOOST_PFR_HAS_STD_MODULE
+import std;
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
+#endif
+
+#ifdef BOOST_PFR_ATTACH_TO_GLOBAL_MODULE
+extern "C++" {
+#include <boost/pfr.hpp>
+}
+#else
+#include <boost/pfr.hpp>
+#endif

module/usage_sample.cpp

@@ -0,0 +1,31 @@
+// Copyright (c) 2016-2024 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=pfr.pcm pfr.pcm usage_sample.cpp
+
+//[pfr_module_example
+#include <iostream>
+#include <iomanip>
+#include <string>
+
+import Boost.PFR;
+
+struct some_person {
+    std::string name;
+    unsigned birth_year;
+};
+
+int main() {
+    some_person val{"Edgar Allan Poe", 1809};
+
+    std::cout << boost::pfr::get<0>(val)                // No macro!
+        << " was born in " << boost::pfr::get<1>(val);  // Works with any aggregate!
+
+    std::cout << '\n' << boost::pfr::io(val);           // Outputs: {"Edgar Allan Poe", 1809}
+    std::cout << "\n." << boost::pfr::get_name<0, some_person>()
+        << '=' << val.name << '\n';                     // Outputs: .name=Edgar Allan Poe
+}
+//]

module/usage_test_mu1.cpp

@@ -0,0 +1,27 @@
+// Copyright (c) 2016-2024 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=pfr.pcm pfr.pcm usage_sample.cpp
+
+#include <iostream>
+
+#include <boost/pfr.hpp>
+
+struct some_person {
+    std::string name;
+    unsigned birth_year;
+};
+
+void mu1_act() {
+    some_person val{"Edgar Allan Poe", 1809};
+
+    std::cout << boost::pfr::get<0>(val)                // No macro!
+        << " was born in " << boost::pfr::get<1>(val);  // Works with any aggregate!
+
+    std::cout << '\n' << boost::pfr::io(val);           // Outputs: {"Edgar Allan Poe", 1809}
+    std::cout << "\n." << boost::pfr::get_name<0, some_person>()
+        << '=' << val.name << '\n';                     // Outputs: .name=Edgar Allan Poe
+}

module/usage_test_mu2.cpp

@@ -0,0 +1,32 @@
+// Copyright (c) 2016-2024 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=pfr.pcm pfr.pcm usage_sample.cpp
+
+#include <iostream>
+#include <iomanip>
+
+import Boost.PFR;
+
+struct some_person {
+    std::string name;
+    unsigned birth_year;
+};
+
+void mu1_act();
+
+int main() {
+    mu1_act();
+
+    some_person val{"Joseph Brodsky", 1940};
+
+    std::cout << boost::pfr::get<0>(val)                // No macro!
+        << " was born in " << boost::pfr::get<1>(val);  // Works with any aggregate!
+
+    std::cout << '\n' << boost::pfr::io(val);
+    std::cout << "\n." << boost::pfr::get_name<0, some_person>()
+        << '=' << val.name << '\n';
+}