C++Talk.NET

Michael Norrish · Guest

I'm confused by g++ 4.0.3's behaviour on the following program (and
its variants, indicated by comments):

----------------------------------------------------------------------
#include <iostream>
using namespace std;

namespace m0 {
namespace m {
class C { public: int x; };
}
}

namespace p {
template <class T> class Foo {
public:
T x;
int g() { return f(x); }
};
}

int h()
{
p::Foo<m0::m::C> foo;
return foo.g();
}

int main()
{
cout << h() << endl;
return 0;
}

namespace m0 {
// this works
namespace m {
int f (C &c) { cout << "Yay\n"; return 1; }
}
// but this does not
// int f(m::C &c) { cout << "Urk\n"; return 2; }
}

// this would also work (if m0::m::f isn't also around - if both are
// present, there is an ambiguous overloading error)
// int f(m0::m::C &c) { cout << "Cool\n"; return 3; }
----------------------------------------------------------------------

The first f (in m0::m) is found because it's in the same namespace as
the declaration of C.

The last f (commented out), is found by name resolution of the
template body, because it appears "in the namespace" of the template
definition. (Indeed, you can mask it by putting a declaration of f
into namespace p.) Of course, the last f is actually in the global
namespace, not in p, but p 'inherits' it.

The second f (commented out) is not found however, and this confuses
me. Why is the rule different for the namespaces associated with the
class argument as opposed to the template definition? I don't get any
inspiration from reading the language of 3.4.2 para 2, and 14.6.4.2)

Or is g++ just incorrect?

Thanks,
Michael.

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