A couple of weeks ago, I merged C++23's P2465R3 Standard Library Modules into microsoft/STL's main branch, which will ship in VS 2022 17.5 Preview 1. Compiler work to fix various ICEs is still ongoing, and build system work is still necessary, but the library work is done. The PR was microsoft/STL#3108 , which begins with: "I've added over 3,750 occurrences of _EXPORT_STD after auditing over 148,000 lines of headers." (That's my STL-internal macro that expands to export, not for users to use directly.) You can try this right now with the VS 2022 17.4 Preview 2 compiler, by building microsoft/STL main. Here's a quick example comparing #include to import std;: D:\GitHub\STL\out\build\x64>type paleolithic_era.cpp #include int main() { std::cout << "Goodbye, header world!\n"; } D:\GitHub\STL\out\build\x64>cl /EHsc /nologo /W4 /std:c++latest /MTd /Od /Bt paleolithic_era.cpp paleolithic_era.cpp time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c1xx.dll)=0.513s time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c2.dll)=0.010s [...linker timings omitted for brevity...] D:\GitHub\STL\out\build\x64>paleolithic_era Goodbye, header world! D:\GitHub\STL\out\build\x64>type new_world_order.cpp import std; int main() { std::cout << "Hello, modules world!\n"; } D:\GitHub\STL\out\build\x64>cl /EHsc /nologo /W4 /std:c++latest /MTd /Od /Bt /c D:\GitHub\STL\out\build\x64\out\modules\std.ixx std.ixx time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c1xx.dll)=2.564s time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c2.dll)=0.204s D:\GitHub\STL\out\build\x64>dir std.ifc std.obj | grep -P "\.ifc|\.obj" 10/10/2022 05:31 PM 28,156,007 std.ifc 10/10/2022 05:31 PM 7,211,607 std.obj D:\GitHub\STL\out\build\x64>cl /EHsc /nologo /W4 /std:c++latest /MTd /Od /Bt new_world_order.cpp std.obj new_world_order.cpp time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c1xx.dll)=0.131s time(C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.34.31823\bin\HostX64\x64\c2.dll)=0.006s [...linker timings omitted for brevity...] D:\GitHub\STL\out\build\x64>new_world_order Hello, modules world! What this shows (as a very quick and dirty benchmark, no attempt to run repeatedly and average timings) is: #include followed by Hello World usage of cout takes 513 ms of compiler front-end time (on my 5950X machine). Building the entire C++ Standard Library into a named module, which needs to be done only once for a given compiler toolset version and project command line, takes 2,564 ms of front-end time (and another 204 ms of back-end time for codegen; this is non-optimized debug mode). This is slightly slower than building a PCH (not depicted here), but not by much. import std; followed by Hello World cout takes only 131 ms of compiler front-end time. That is, importing the entire C++ Standard Library as a named module is 3.9x faster (times, not percent) than classic inclusion of . This speedup will naturally vary depending on what a real program is doing (including more headers will make the classic inclusion scenario much slower - is big but not the biggest - while doing more actual work in the source file will dilute the raw performance difference), but I think this effectively shows how simple (one import!) and fast the Standard Library Modules will be. There are other advantages (macro immunity, not leaking internal names) too. Finally, note that this is very space-efficient - the digested IFC file that allows this rapid importation is only 26.9 MB, plus another 6.9 MB for the OBJ - in previous measurements I've seen that this is about 10x smaller than a PCH. More on reddit.com

The libstdc++ one is passable. For instance here is the doc of std::copy : /** * @brief Copy the elements of a sequence for which a predicate is true. * @ingroup mutating_algorithms * @param __first An input iterator. * @param __last An input iterator. * @param __result An output iterator. * @param __pred A predicate. * @return An iterator designating the end of the resulting sequence. * * Copies each element in the range @p [__first,__last) for which * @p __pred returns true to the range beginning at @p __result. * * copy_if() is stable, so the relative order of elements that are * copied is unchanged. */ More on reddit.com