[v3 PATCH] PR libstdc++/79141

[Jonathan Wakely]

On 03/04/17 16:43 +0100, Jonathan Wakely wrote:
>On 02/04/17 02:45 +0300, Ville Voutilainen wrote:
>>   PR libstdc++/79141
>>   * include/bits/stl_pair.h (__wrap_nonesuch): New.
>>   (operator=(typename conditional<
>>   __and_<is_copy_assignable<_T1>,
>>   is_copy_assignable<_T2>>::value,
>>   const pair&, const __wrap_nonesuch&>::type)): Change __nonesuch
>>   to __wrap_nonesuch.
>>   (operator=(typename conditional<
>>   __not_<__and_<is_copy_assignable<_T1>,
>>   is_copy_assignable<_T2>>>::value,
>>   const pair&, const __nonesuch&>::type)): Likewise.
>>   (operator=(typename conditional<
>>   __and_<is_move_assignable<_T1>,
>>   is_move_assignable<_T2>>::value,
>>   pair&&, __wrap_nonesuch&&>::type)): Likewise.
>>   * testsuite/20_util/pair/79141.cc: New.
>
>>diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h
>>index 7c7cee2..b746fb4 100644
>>--- a/libstdc++-v3/include/bits/stl_pair.h
>>+++ b/libstdc++-v3/include/bits/stl_pair.h
>>@@ -179,6 +179,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>      }
>>  };
>>
>>+  struct __wrap_nonesuch : std::__nonesuch {
>>+    explicit __wrap_nonesuch(const __nonesuch&) = delete;
>>+  };
>
>Could you please add a comment explaining that this is needed to
>ensure that functions with parameters of this type are not viable when
>an argument of {} is used. Because even with such a comment I'll
>probably not understand this by next week.
>
>And I think __explicit_nonesuch or __no_list_init would be a clearer
>name. We're not really "wrapping" this, unless I misunderstand.
>
>OK for trunk, I suppose.

Oh, and gcc-6-branch.