[committed] libstdc++: Allow visiting inherited variants [PR 90943]

[Jonathan Wakely]

On Sun, 3 Oct 2021 at 10:07, Jonathan Wakely wrote:
>
>
>
> On Sat, 2 Oct 2021, 13:50 Daniel Krügler via Libstdc++, <libstdc++@gcc.gnu.org> wrote:
>>
>> Am Fr., 1. Okt. 2021 um 21:57 Uhr schrieb Jonathan Wakely via
>> Libstdc++ <libstdc++@gcc.gnu.org>:
>> >
>> > Implement the changes from P2162R2 (as a DR for C++17).
>> >
>> > Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> >         PR libstdc++/90943
>> >         * include/std/variant (__cpp_lib_variant): Update value.
>> >         (__detail::__variant::__as): New helpers implementing the
>> >         as-variant exposition-only function templates.
>> >         (visit, visit<R>): Use __as to upcast the variant parameters.
>> >         * include/std/version (__cpp_lib_variant): Update value.
>> >         * testsuite/20_util/variant/visit_inherited.cc: New test.
>> >
>> > Tested powerpc64le-linux. Committed to trunk.
>> >
>>
>> I'm wondering why the first __as overload is not noexcept as well (or
>> asking it the other way around: Why different exception-specifications
>> are used for the different overloads):
>>
>> +  // The __as function templates implement the exposition-only "as-variant"
>> +
>> +  template<typename... _Types>
>> +    constexpr std::variant<_Types...>&
>> +    __as(std::variant<_Types...>& __v)
>> +    { return __v; }
>
>
> Probably just an oversight, I'll check again and fix it. Thanks!

Fixed by the attached patch, thanks again.

Tested powerpc64le-linux, pushed to trunk.
-------------- next part --------------
commit 728e639d82099035fdfe69b716a54717ae7050e0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Oct 4 10:21:58 2021

    libstdc++: Add missing noexcept to std::variant helper
    
    libstdc++-v3/ChangeLog:
    
            * include/std/variant (__detail::__variant::__as): Add missing
            noexcept to first overload.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index d50c6b7de1d..6377b6731ea 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -206,7 +206,7 @@ namespace __variant
 
   template<typename... _Types>
     constexpr std::variant<_Types...>&
-    __as(std::variant<_Types...>& __v)
+    __as(std::variant<_Types...>& __v) noexcept
     { return __v; }
 
   template<typename... _Types>