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

[Jonathan Wakely]

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!

I won't repeat my questions for your is_virtual_base_of patch,
regarding the legal prerequisites, but they apply here too. My
comments about copyright and licence headers in the tests apply here
too.

+#if __cplusplus > 202302L
+  // const string & + string_view

Please test the feature test macro, not the C++ standard version, so e.g.

#if __glibcxx_string_view >= 202403L

This relates the #if block directly to the feature test macro, so that
if we decide to support the feature in C++23 as an extension, we only
need to change version.def and not basic_string.h