[Bug libstdc++/44436] [C++0x] Implement emplace* in associative and unordered containers

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44436

--- Comment #28 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-06-09 
13:27:56 UTC ---
(In reply to comment #26)
> For map, the first argument to emplace is going to be the key (I believe).  We
> can therefore determine if the key is already present in the map before we
> construct the value object from the remaining arguments to emplace.

Not necessarily:

std::map<int, int> m;
m.emplace(piecewise_construct_t, make_tuple(1), make_tuple(2));