libstdc++/4051 is not a bug

[Philip Martin]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=4051&database=gcc

You have implemented the output operator for std::pair<int,int> in the
global namespace, but you are attempting to use it via std::copy in
the std namespace. Only the std namespace will be searched for an
output operator. The complier correctly reports no match.

Argument-dependent name lookup (3.4.2 [basic.lookup.koenig]) for a
template id applies to the search for the output operator, allowing
the output operator to be defined in the same namespace as the
template or the template arguments. Thus when one of the std::pair is
of class type, the namespace of the class will also be searched and so
you have no problem.

Philip