[Bug libstdc++/55043] [4.7/4.8 Regression] issue with nesting unordered_map containing unique_ptr into vector

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55043



--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-10-24 
01:08:13 UTC ---

It already does use move_if_noexcept, so should work.



The problem is that

std::is_copy_constructible<std::unordered_set<std::unique_ptr<int>>>::value is

true, so __move_if_noexcept_cond is true for unordered containers and we try to

copy them.



That happens because this is well-formed:



    typedef std::unordered_set<std::unique_ptr<int>> S;

    decltype(::new S(std::declval<const S&>())) s;



That should be ill-formed, but for some reason isn't when it occurs as an

unevaluated operand.



This is ill-formed, as expected:



    S ss;

    ::new S(static_cast<const S&>(ss));