[v3 PATCH] Implement LWG 2729 for pair.

[Jonathan Wakely]

On 17/08/16 07:41 +0300, Ville Voutilainen wrote:
>    Implement LWG 2729 for pair.
>    * include/bits/stl_pair.h (_PCC): New.
>    (_ConstructiblePair, _ImplicitlyConvertiblePair):
>    Turn into static member functions of _PCC.
>    (_MoveConstructiblePair, _ImplicitlyMoveConvertiblePair): Likewise.
>    (_PCCP): New.
>    (pair(const _T1&, const _T2&)): Adjust.
>    (_PCCFP): New.
>    (pair(const pair<_U1, _U2>&)): Adjust.
>    (pair(_U1&&, const _T2&)): Likewise.
>    (pair(const _T1&, _U2&&)): Likewise.
>    (pair(_U1&&, _U2&&)): Likewise.
>    (pair(pair<_U1, _U2>&&)): Likewise.
>    (operator=(const pair&)): Make conditionally deleted.
>    (operator=(pair&&)): Make conditionally suppressed.
>    (operator=(const pair<_U1, _U2>&)): Constrain.
>    (operator=(pair<_U1, _U2>&&): Likewise.
>    * include/std/type_traits (__nonesuch): New.
>    * testsuite/20_util/pair/traits.cc: Likewise.

I found the "Likewise" a bit confusing here. I realise it means "New"
but my first thought was it meant you were adding __nonesuch to that
test file. "New" for the test would be unambiguous :-)

>diff --git a/libstdc++-v3/testsuite/20_util/pair/traits.cc b/libstdc++-v3/testsuite/20_util/pair/traits.cc
>new file mode 100644
>index 0000000..0989cf1
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/20_util/pair/traits.cc
>@@ -0,0 +1,77 @@
>+// { dg-do compile }
>+// { dg-options "-std=gnu++11" }

This patch predates my testsuite changes, so this should now be
{ dg-do compile { target c++11 } } 

Otherwise OK for trunk, thanks.