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gsl_byte should inspect __cpp_lib_byte in addition to _HAS_STD_BYTE #821

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gsl_byte should inspect __cpp_lib_byte in addition to _HAS_STD_BYTE#821
@StephanTLavavej

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@StephanTLavavej
StephanTLavavej
opened on Oct 24, 2019

GSL/include/gsl/gsl_byte

Lines 43 to 54 in 3d56ba9

#ifndef GSL_USE_STD_BYTE
// this tests if we are under MSVC and the standard lib has std::byte and it is enabled
#if defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
#define GSL_USE_STD_BYTE 1
#else // defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
#define GSL_USE_STD_BYTE 0
#endif // defined(_HAS_STD_BYTE) && _HAS_STD_BYTE
#endif // GSL_USE_STD_BYTE

inspects an implementation-specific macro _HAS_STD_BYTE defined by MSVC's STL:

https://github.com/microsoft/STL/blob/447f879b136950baf3ca35dfb54c359494fa2a77/stl/inc/yvals_core.h#L475-L477

instead of the Standard feature-test macro __cpp_lib_byte:

https://github.com/microsoft/STL/blob/447f879b136950baf3ca35dfb54c359494fa2a77/stl/inc/yvals_core.h#L888-L890

GSL could inspect both, which would make it compatible with:

  • VS 2017 15.3 (which added std::byte and _HAS_STD_BYTE) through 15.7
  • VS 2017 15.8 (which added __cpp_lib_byte) through VS 2019 today
  • Future versions of VS (when GSL stops inspecting _HAS_STD_BYTE alone, VS can stop defining it).

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