On Mon, Oct 13, 2025 at 5:09 PM Patrick Palka <[email protected]> wrote:

> Series tested on x86_64-pc-linux-gnu, does this look OK for trunk only?
>
> -- >8 --
>
> This FTM is like __cpp_explicit_this_parameter but is also defined
> in earlier C++ modes if deducing this is supported as an extension
> by the compiler.  Currently only GCC supports this, Clang doesn't.
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/c++config (_GLIBCXX_EXPLICIT_THIS_PARAMETER):
>         New.
> ---
>
As discussed,  adjust the macro definition later, so this LGTM outside one
comment.



>  libstdc++-v3/include/bits/c++config | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/libstdc++-v3/include/bits/c++config
> b/libstdc++-v3/include/bits/c++config
> index eec3a4a499dd..e6d8f186d0d4 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -927,6 +927,13 @@ namespace __gnu_cxx
>  # define _GLIBCXX_USE_BUILTIN_TRAIT(BT) 0
>  #endif
>
> +// Whether deducing this is usable either officially, if in C++23 mode, or
> +// as an extension (Clang doesn't support the latter).
> +#if __cpp_explicit_this_parameter \
> +  || (__cplusplus >= 201103L && __GNUC__ >= 14 &&
> !defined(_GLIBCXX_CLANG))
>
We always target only the version of GCC that we are compiled with, as far
as I understand,
so we could just make this #if __cpp_explicit_this_parameter &&
!defined(_GLIBCXX_CLANG)?

> +# define _GLIBCXX_EXPLICIT_THIS_PARAMETER 202110L
> +#endif
> +
>  // Mark code that should be ignored by the compiler, but seen by Doxygen.
>  #define _GLIBCXX_DOXYGEN_ONLY(X)
>
> --
> 2.51.0.491.g4b71b29477
>
>

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