[Bug libstdc++/52942] [4.7 Regression] using std::ref with a std::unordered_map fails to compile

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52942

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |libstdc++
           Severity|major                       |normal

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-04-12 
08:40:06 UTC ---
unordered_map derives privately from its template _ExtractKey parameter which
is _Select1st and provides argument_type.

If G++ checked access control in SFINAE situations I believe the code would
work, as __has_argument_type would not report an access failure, unfortunately
that isn't implemented in G++