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C++20 module support #255

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C++20 module support #255

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38386f0
Initial impl
anarthal Feb 27, 2026
1cab823
Remaining headers
anarthal Feb 27, 2026
ae1ef02
compat headers
anarthal Feb 27, 2026
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11 changes: 10 additions & 1 deletion CMakeLists.txt
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Expand Up @@ -3,7 +3,7 @@
# Distributed under the Boost Software License, Version 1.0.
# https://www.boost.org/LICENSE_1_0.txt

cmake_minimum_required(VERSION 3.8...3.20)
cmake_minimum_required(VERSION 3.8...3.31)

project(boost_charconv VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)

Expand All @@ -14,6 +14,15 @@ add_library(boost_charconv

add_library(Boost::charconv ALIAS boost_charconv)

if (BOOST_USE_MODULES)
target_sources(boost_charconv PUBLIC FILE_SET CXX_MODULES BASE_DIRS modules FILES modules/boost_charconv.cppm)

# Enable and propagate C++23, import std, and the modules macro
target_compile_features(boost_charconv PUBLIC cxx_std_23)
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@mborland mborland Jan 13, 2025

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Have you tried this with C++20 instead of 23? I know officially import std and import std.compat are C++23, but all of the compiler implementors have said they'll allow it at 20.

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@anarthal anarthal Jan 13, 2025

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Do you think there's a use to it? My understanding was that using C++20 over C++23 is about being able to use older compilers that might not support C++23. Such compilers won't have proper module implementations, likely, since modules are quite behind everything else.

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@mborland mborland Jan 13, 2025

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Standards like MISRA are pinned to language standards not toolchains. Theoretically someone could have a modern compiler but be stuck at C++20. Probably best to have someone in the real world complain before changing it.

set_target_properties(boost_charconv PROPERTIES CXX_MODULE_STD 1)
target_compile_definitions(boost_charconv PUBLIC BOOST_USE_MODULES)
endif()

target_include_directories(boost_charconv PUBLIC include)


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17 changes: 16 additions & 1 deletion include/boost/charconv/chars_format.hpp
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Expand Up @@ -5,11 +5,24 @@
#ifndef BOOST_CHARCONV_CHARS_FORMAT_HPP
#define BOOST_CHARCONV_CHARS_FORMAT_HPP

#if defined(BOOST_USE_MODULES) && !defined(BOOST_CHARCONV_INTERFACE_UNIT)

#ifndef BOOST_IN_MODULE_PURVIEW
import boost.charconv;
#ifndef BOOST_CHARCONV_CONSTEXPR
#define BOOST_CHARCONV_CONSTEXPR constexpr
#endif
#endif

#else

#include <boost/charconv/config.hpp>

namespace boost { namespace charconv {

// Floating-point format for primitive numerical conversion
// chars_format is a bitmask type (16.3.3.3.3)
enum class chars_format : unsigned
BOOST_CHARCONV_MODULE_EXPORT enum class chars_format : unsigned
{
scientific = 1 << 0,
fixed = 1 << 1,
Expand All @@ -19,4 +32,6 @@ enum class chars_format : unsigned

}} // Namespaces

#endif // defined(BOOST_USE_MODULES) && !defined(BOOST_CHARCONV_INTERFACE_UNIT)

#endif // BOOST_CHARCONV_CHARS_FORMAT_HPP
14 changes: 13 additions & 1 deletion include/boost/charconv/config.hpp
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@@ -1,3 +1,8 @@
// Make the header safe to include from libraries supporting modules
#if defined(BOOST_IN_MODULE_PURVIEW) && !defined(BOOST_CHARCONV_CONFIG_HPP_INCLUDED)
# error "Please #include <boost/charconv/config.hpp> in your module global fragment"
#endif

#ifndef BOOST_CHARCONV_CONFIG_HPP_INCLUDED
#define BOOST_CHARCONV_CONFIG_HPP_INCLUDED

Expand All @@ -7,7 +12,7 @@
// https://www.boost.org/LICENSE_1_0.txt

#include <boost/config.hpp>
#include <climits>
#include <boost/config/std/climits.hpp>

// This header implements separate compilation features as described in
// http://www.boost.org/more/separate_compilation.html
Expand Down Expand Up @@ -36,4 +41,11 @@

#endif

// Modules
#ifdef BOOST_USE_MODULES
# define BOOST_CHARCONV_MODULE_EXPORT export
#else
# define BOOST_CHARCONV_MODULE_EXPORT
#endif

#endif // BOOST_CHARCONV_CONFIG_HPP_INCLUDED
2 changes: 1 addition & 1 deletion include/boost/charconv/detail/apply_sign.hpp
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Expand Up @@ -8,7 +8,7 @@
#include <boost/config.hpp>
#include <boost/charconv/detail/emulated128.hpp>
#include <boost/charconv/detail/type_traits.hpp>
#include <type_traits>
#include <boost/config/std/type_traits.hpp>

// We are purposefully converting values here
#ifdef BOOST_MSVC
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4 changes: 2 additions & 2 deletions include/boost/charconv/detail/bit_layouts.hpp
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Expand Up @@ -7,8 +7,8 @@

#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/detail/emulated128.hpp>
#include <cstdint>
#include <cfloat>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cfloat.hpp>

// Layouts of floating point types as specified by IEEE 754
// See page 23 of IEEE 754-2008
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2 changes: 1 addition & 1 deletion include/boost/charconv/detail/buffer_sizing.hpp
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Expand Up @@ -7,7 +7,7 @@

#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/detail/integer_search_trees.hpp>
#include <type_traits>
#include <boost/config/std/type_traits.hpp>

namespace boost {
namespace charconv {
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6 changes: 3 additions & 3 deletions include/boost/charconv/detail/compute_float32.hpp
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Expand Up @@ -6,9 +6,9 @@
#define BOOST_CHARCONV_DETAIL_COMPUTE_FLOAT32_HPP

#include <boost/charconv/detail/compute_float64.hpp>
#include <limits>
#include <cstdint>
#include <cmath>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cmath.hpp>

namespace boost { namespace charconv { namespace detail {

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8 changes: 4 additions & 4 deletions include/boost/charconv/detail/compute_float64.hpp
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Expand Up @@ -10,10 +10,10 @@
#include <boost/charconv/detail/significand_tables.hpp>
#include <boost/charconv/detail/emulated128.hpp>
#include <boost/core/bit.hpp>
#include <cstdint>
#include <cfloat>
#include <cstring>
#include <cmath>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cfloat.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/cmath.hpp>

namespace boost { namespace charconv { namespace detail {

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18 changes: 9 additions & 9 deletions include/boost/charconv/detail/compute_float80.hpp
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Expand Up @@ -8,17 +8,17 @@
#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/detail/emulated128.hpp>
#include <boost/charconv/detail/bit_layouts.hpp>
#include <system_error>
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cmath>
#include <climits>
#include <cfloat>
#include <boost/config/std/system_error.hpp>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cmath.hpp>
#include <boost/config/std/climits.hpp>
#include <boost/config/std/cfloat.hpp>

#ifdef BOOST_CHARCONV_DEBUG_FLOAT128
#include <iostream>
#include <iomanip>
#include <boost/config/std/iostream.hpp>
#include <boost/config/std/iomanip.hpp>
#include <boost/charconv/detail/to_chars_integer_impl.hpp>
#endif

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11 changes: 8 additions & 3 deletions include/boost/charconv/detail/config.hpp
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Expand Up @@ -2,12 +2,17 @@
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

// Make this header safe to include in our purview
#if defined(BOOST_IN_MODULE_PURVIEW) && !defined(BOOST_CHARCONV_DETAIL_CONFIG_HPP)
# error "Please #include <boost/charconv/detail/config.hpp> in your module global fragment"
#endif

#ifndef BOOST_CHARCONV_DETAIL_CONFIG_HPP
#define BOOST_CHARCONV_DETAIL_CONFIG_HPP

#include <boost/config.hpp>
#include <type_traits>
#include <cfloat>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/cfloat.hpp>

#include <boost/assert.hpp>
#define BOOST_CHARCONV_ASSERT(expr) BOOST_ASSERT(expr)
Expand Down Expand Up @@ -169,7 +174,7 @@ static_assert((BOOST_CHARCONV_ENDIAN_BIG_BYTE || BOOST_CHARCONV_ENDIAN_LITTLE_BY
// All of these types are optional so check for each of them individually
#if (defined(_MSVC_LANG) && _MSVC_LANG > 202002L) || __cplusplus > 202002L
# if __has_include(<stdfloat>)
# include <stdfloat>
# include <boost/config/std/stdfloat.hpp>
# endif
#endif
#ifdef __STDCPP_FLOAT16_T__
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8 changes: 4 additions & 4 deletions include/boost/charconv/detail/dragonbox/dragonbox.hpp
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Expand Up @@ -30,10 +30,10 @@
#include <boost/charconv/detail/to_chars_result.hpp>
#include <boost/charconv/chars_format.hpp>
#include <boost/core/bit.hpp>
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cstring>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstring.hpp>

#ifdef BOOST_MSVC
# pragma warning(push)
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12 changes: 6 additions & 6 deletions include/boost/charconv/detail/dragonbox/dragonbox_common.hpp
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Expand Up @@ -29,12 +29,12 @@
#include <boost/charconv/detail/emulated128.hpp>
#include <boost/charconv/chars_format.hpp>
#include <boost/core/bit.hpp>
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cstring>
#include <cstddef>
#include <climits>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/cstddef.hpp>
#include <boost/config/std/climits.hpp>

namespace boost { namespace charconv { namespace detail {

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12 changes: 6 additions & 6 deletions include/boost/charconv/detail/dragonbox/floff.hpp
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Expand Up @@ -31,12 +31,12 @@
#include <boost/charconv/detail/to_chars_result.hpp>
#include <boost/charconv/chars_format.hpp>
#include <boost/core/bit.hpp>
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cstring>
#include <cstddef>
#include <climits>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/cstddef.hpp>
#include <boost/config/std/climits.hpp>

#ifdef BOOST_MSVC
# pragma warning(push)
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10 changes: 5 additions & 5 deletions include/boost/charconv/detail/emulated128.hpp
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Expand Up @@ -11,11 +11,11 @@
#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/config.hpp>
#include <boost/core/bit.hpp>
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cassert>
#include <cmath>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/limits.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cassert.hpp>
#include <boost/config/std/cmath.hpp>

namespace boost { namespace charconv { namespace detail {

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12 changes: 6 additions & 6 deletions include/boost/charconv/detail/fallback_routines.hpp
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Expand Up @@ -10,12 +10,12 @@
#include <boost/charconv/detail/config.hpp>
#include <boost/charconv/detail/from_chars_result.hpp>
#include <boost/charconv/chars_format.hpp>
#include <system_error>
#include <type_traits>
#include <locale>
#include <clocale>
#include <cstring>
#include <cstdio>
#include <boost/config/std/system_error.hpp>
#include <boost/config/std/type_traits.hpp>
#include <boost/config/std/locale.hpp>
#include <boost/config/std/clocale.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/cstdio.hpp>

namespace boost {
namespace charconv {
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8 changes: 4 additions & 4 deletions include/boost/charconv/detail/fast_float/ascii_number.hpp
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Expand Up @@ -9,10 +9,10 @@
#define BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP

#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <cctype>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <boost/config/std/cctype.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/iterator.hpp>

namespace boost { namespace charconv { namespace detail { namespace fast_float {

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8 changes: 4 additions & 4 deletions include/boost/charconv/detail/fast_float/bigint.hpp
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Expand Up @@ -9,10 +9,10 @@
#define BOOST_CHARCONV_DETAIL_FASTFLOAT_BIGINT_HPP

#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <algorithm>
#include <cstdint>
#include <climits>
#include <cstring>
#include <boost/config/std/algorithm.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/climits.hpp>
#include <boost/config/std/cstring.hpp>

namespace boost { namespace charconv { namespace detail { namespace fast_float {

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5 changes: 5 additions & 0 deletions include/boost/charconv/detail/fast_float/constexpr_feature_detect.hpp
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Expand Up @@ -5,6 +5,11 @@
//
// Derivative of: https://github.com/fastfloat/fast_float

// Make the header safe to include from libraries supporting modules
#if defined(BOOST_IN_MODULE_PURVIEW) && !defined(BOOST_CHARCONV_DETAIL_FASTFLOAT_CONSTEXPR_FEATURE_DETECT_HPP)
# error "Please #include <boost/charconv/detail/fast_float/constexpr_feature_support.hpp> in your module global fragment"
#endif

#ifndef BOOST_CHARCONV_DETAIL_FASTFLOAT_CONSTEXPR_FEATURE_DETECT_HPP
#define BOOST_CHARCONV_DETAIL_FASTFLOAT_CONSTEXPR_FEATURE_DETECT_HPP

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12 changes: 6 additions & 6 deletions include/boost/charconv/detail/fast_float/decimal_to_binary.hpp
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Expand Up @@ -10,12 +10,12 @@

#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <boost/charconv/detail/fast_float/fast_table.hpp>
#include <cfloat>
#include <cinttypes>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <boost/config/std/cfloat.hpp>
#include <boost/config/std/cinttypes.hpp>
#include <boost/config/std/cmath.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstdlib.hpp>
#include <boost/config/std/cstring.hpp>

namespace boost { namespace charconv { namespace detail { namespace fast_float {

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8 changes: 4 additions & 4 deletions include/boost/charconv/detail/fast_float/digit_comparison.hpp
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Expand Up @@ -11,10 +11,10 @@
#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <boost/charconv/detail/fast_float/bigint.hpp>
#include <boost/charconv/detail/fast_float/ascii_number.hpp>
#include <algorithm>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <boost/config/std/algorithm.hpp>
#include <boost/config/std/cstdint.hpp>
#include <boost/config/std/cstring.hpp>
#include <boost/config/std/iterator.hpp>

namespace boost { namespace charconv { namespace detail { namespace fast_float {

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2 changes: 1 addition & 1 deletion include/boost/charconv/detail/fast_float/fast_table.hpp
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Expand Up @@ -9,7 +9,7 @@
#define BOOST_CHARCONV_DETAIL_FASTFLOAT_FAST_TABLE_HPP

#include <boost/charconv/detail/fast_float/float_common.hpp>
#include <cstdint>
#include <boost/config/std/cstdint.hpp>

namespace boost { namespace charconv { namespace detail { namespace fast_float {

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