GCC/Clang против MSVC: отсутствует предупреждение Wconversion в функции шаблона с помощью std::invoke ⇐ C++

[Anonymous]

I'm encountering an issue where a template function uses std::invoke to call another function, passing a size_t argument to a parameter expecting an int32_t. This should, theoretically, trigger a warning about type conversion. However, when compiling with GCC or Clang using the -Wconversion flag, no warning is issued, whereas MSVC correctly reports a warning.

Here's a simplified version of the code:

void expectsInt32(int32_t) { /* … */ } template void call(Func func, Arg arg) { std::invoke(func, arg); // arg is size_t, potentially causing narrowing conversion } int main() { size_t largeNumber = 4294967295; // Maximum value for uint32_t call(expectsInt32, largeNumber); // Compiles without warning in GCC/Clang with -Wconversion return 0; } On MSVC, this code triggers a warning about the potential data loss during the conversion from size_t to int32_t:

C:/data/msvc/14.39.33321-Pre/include\type_traits(1739): error C2220: the following warning is treated as an error C:/data/msvc/14.39.33321-Pre/include\type_traits(1739): warning C4267: 'argument': conversion from 'size_t' to 'int32_t', possible loss of data C:/data/msvc/14.39.33321-Pre/include\type_traits(1739): note: the template instantiation context (the oldest one first) is (18): note: see reference to function template instantiation 'void call(Func,Arg)' being compiled with [ Func=void (__cdecl *)(int32_t), Arg=size_t ] (12): note: see reference to function template instantiation 'void std::invoke(_Callable,_Ty1) noexcept(false)' being compiled with [ Arg=size_t, _Callable=void (__cdecl *&)(int32_t), _Ty1=size_t & ] Compiler returned: 2 However, the same warning is not emitted by GCC or Clang, even with the -Wconversion flag enabled.

Why might GCC/Clang not warn about this implicit conversion in the context of std::invoke with template arguments? Is there a way to enforce such warnings or add static assertions to catch these cases at compile time?

Here's the code reproduced on Compiler Explorer: https://godbolt.org/z/KPPYM8cna


Источник: https://stackoverflow.com/questions/781 ... -with-stdi