Re: [GSoC] Conflicted Built-in Trait Name

[Jonathan Wakely <jwakely@redhat.com>]

On Sat, 25 Mar 2023 at 12:23, Roy Jacobson via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Clang has been providing __is_void for a very long time now, and is
> definitely compatible with libstdc++. Does defining this builtin cause a
> problem? Might be that the lookup rules for builtins are different or
> something.
>
> https://clang.llvm.org/docs/LanguageExtensions.html#type-trait-primitives

Clang has special hacks that allow it to handle libstdc++ headers.
When it sees the use of a built-in trait like __is_void used as an
identifier, it disables the built-in and treats it as a normal
identifier for the rest of the translation unit. GCC doesn't do that,
so "it compiles with Clang" isn't really relevant here.


>
> On Sat, 25 Mar 2023 at 15:08, Ken Matsui via Gcc <gcc@gcc.gnu.org> wrote:
>
> > Hi,
> >
> > I am working on the GSoC project, "C++: Implement compiler built-in
> > traits for the standard library traits".
> >
> > Built-in trait naming simply adds two underscores (__) to the original
> > trait name. However, the same names are already in use for some
> > built-in traits, such as is_void, is_pointer, and is_signed.
> >
> > For example, __is_void is used in the following files:
> >
> > * gcc/testsuite/g++.dg/tm/pr46567.C
> > * libstdc++-v3/include/bits/cpp_type_traits.h
> >
> > In this case, are we supposed to change the existing same name in the
> > code to something like ____is_void (four underscores)? Or is it better
> > to break the naming convention of built-in traits like
> > __is_void_builtin?
> >
> > Sincerely,
> > Ken Matsui
> >
>