P0466R5 Layout-Compatibility And Pointer-Interconvertibility Traits

[StephanTLavavej]

P0466R5 Layout-Compatibility And Pointer-Interconvertibility Traits

Feature-test macros as of WG21-N4842:

#define __cpp_lib_is_layout_compatible 201907L
#define __cpp_lib_is_pointer_interconvertible 201907L

This needs compiler support, implemented by Microsoft-internal MSVC-PR-227560 for VS 2019 16.7.

Compiler bugs encountered:

• VSO-1231996 Missing __builtin_* intrinsics helpers for Corresponding Member and Pointer-interconvertibility Traits
  • Fixed for VS 2019 16.9 Preview 2 by MSVC-PR-282455
• VSO-1232619 __builtin_is_pointer_interconvertible_base_of intrinsic returns incorrect values
  • Fixed for VS 2019 16.9 Preview 2 by MSVC-PR-285501