[PATCH v2] libstdc++: implement concatenation of strings and string_views

[Jonathan Wakely]

On Tue, 30 Jul 2024 at 22:54, Giuseppe D'Angelo
<giuseppe.dangelo@kdab.com> wrote:
>
> On 30/07/2024 15:27, Jonathan Wakely wrote:
> > On Tue, 30 Jul 2024 at 14:08, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> >>
> >> On Tue, 30 Jul 2024 at 08:31, Giuseppe D'Angelo
> >> <giuseppe.dangelo@kdab.com> wrote:
> >>>
> >>> Hello!
> >>>
> >>> The attached patch implements adds support for P2591R5 in libstdc++
> >>> (concatenation of strings and string_views, approved in Tokyo for C++26).
> >>
> >> Thanks for this patch as well. This was on my TODO list so I'll be
> >> happy to not have to do it myself now!
>
> Thank you for the thorough review and guidance; I hope I have fixed
> everything, attaching the new patch.

Great, thanks for the quick turnaround.

One more thing that I missed last time, sorry:

+#if __glibcxx_string_view >= 202403L
+  // const string & + string_view
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
+    inline basic_string<_CharT, _Traits, _Alloc>
+    operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
+           __type_identity_t<basic_string_view<_CharT, _Traits>> __rhs)

Since this is a C++26 feature, we can use [[nodiscard]] and constexpr
unconditionally, so it can be simply:

+  template<typename _CharT, typename _Traits, typename _Alloc>
+    [[nodiscard]]
+    constexpr basic_string<_CharT, _Traits, _Alloc>

i.e. use [[nodiscard]] not the NODISCARD macro, and constexpr instead
of the CONSTEXPR macro and the inline keyword.

But I can make those change before committing.

This patch also reminds me that we need to make the changes to replace
__type_element_t with type_element_t, as per your LWG issue to clean
that up.



>
> I don't have committing rights, so feel free to grab the patch and apply
> it at your convenience :)
>
> Thanks,
> --
> Giuseppe D'Angelo
>