Re: [PATCH] libstdc++: use new built-in trait __is_reference

[Xi Ruoyao <xry111@xry111.site>]

On Mon, 2023-03-20 at 00:30 -0700, Ken Matsui wrote:
> I see. Thank you!

Please continue to read.  I guess you missed some inline comments from
me...

> 
> On Mon, Mar 20, 2023 at 12:26 AM Xi Ruoyao <xry111@xry111.site> wrote:
> > 
> > You need to CC libstdc++@gcc.gnu.org for any patches touching
> > libstdc++.
> > 
> > On Sat, 2023-03-18 at 21:21 -0700, Ken Matsui via Gcc-patches wrote:
> > > libstdc++-v3/ChangeLog:
> > > 
> > > * include/std/type_traits (is_reference): Use __is_reference
> > > built-in
> > > trait.
> > 
> > Bad ChangeLog format.  You should have a tab (not 4 or 8 spaces, nor
> > nothing) to indent the ChangeLog content.
> > 
> > Is there any benefit to use a builtin, instead of the existing
> > implementation?  I can see no but maybe I'm stupid.
> > 
> > > ---
> > > diff --git a/libstdc++-v3/include/std/type_traits
> > > b/libstdc++-v3/include/std/type_traits
> > 
> > The patch fails to apply.  It seems because your mail client
> > inserted an
> > additional newline before "b/".  Try to use git-send-email or
> > configure
> > the mail client properly.
> > 
> > > index 2bd607a8b8f..18408d8ceb6 100644
> > > --- a/libstdc++-v3/include/std/type_traits
> > > +++ b/libstdc++-v3/include/std/type_traits
> > > @@ -639,6 +639,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > >    // Composite type categories.
> > > 
> > >    /// is_reference
> > > +#if __has_builtin(__is_reference)
> > > +  template<typename _Tp>
> > > +    struct is_reference
> > > +    : public integral_constant<bool, __is_reference(_Tp)>
> > 
> > If a patch depends on another patch not applied yet, sent them in a
> > series.  Or people are puzzled because when this patch is applied
> > alone,
> > the code fails to build.
> > 
> > > +    { };
> > > +#else
> > >    template<typename _Tp>
> > >      struct is_reference
> > >      : public false_type
> > > @@ -653,6 +659,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > >      struct is_reference<_Tp&&>
> > >      : public true_type
> > >      { };
> > > +#endif
> > > 
> > >    /// is_arithmetic
> > >    template<typename _Tp>
> > 
> > --
> > Xi Ruoyao <xry111@xry111.site>
> > School of Aerospace Science and Technology, Xidian University

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University