In the sample below, if you remove the using declaration and fix up the manipulator to be fully qualified, it works. Otherwise, it fails with an illegal operand type. The sample below works when templates are converted to non-templates. This is probably part of the problem with "using std::endl", which results in an endl template not instantiated error.

namespace ns {

template <class T1> struct A {
A<T1>& operator<<(A<T1>& (*m)(A<T1>&)) { return m(*this); }
};

template <class T2> inline A<T2>& fn(A<T2>& test) { return test; }

} //ns

using ns::fn;

int main() {
ns::A<int> a;
a << fn;
// Error: illegal operand types
// Had: ns::A<>
}

Richard