C++ ADL: Call a function from the namespace which a particular type belongs to

Question

Imagine there is an existing type Inner in its own namespace. In this namespace there is a function/operator ( myfunc ) taking in the Inner type. Suppose, this function doesn't work properly, but we can't change it. Next, the type Inner is aliased within another class ( G ). That class belongs to a different namespace and defines a proper version of myfunc there. There is also a class template parametrized by G . When it calls myfunc ADL automatically selects the namespace of Inner . Is it possible to tell the compiler that it should call myfunc from the namespace of G ?

namespace ns1
{
    template <class T>
    class F
    {
    public:
        F()
        {
            typename T::I inner;

            // myfunc() is declared both in the namespace of T and T::I.
            // ADL picks up the innermost, i.e. T::I. Is it possible to 
            // tell the compiler that myfunc() must be selected from the 
            // namespace of T?
            myfunc(inner);
        }
    };
}

namespace ns3
{
    class Inner { };

    void myfunc(const Inner& i) {}
}

namespace ns2
{
    class G
    {
    public:
        using I = ns3::Inner;
    };
}

int main()
{
    ns1::F<ns2::G> f;
}

Generally speaking, is there any way in C++ to access the namespace of a particular entity? Eg namespace_of(SomeClass)::function_in_that_namespace() .

Answer 1

Is it possible to tell the compiler that it should call myfunc from the namespace of G ?

No.

Generally speaking, is there any way in C++ to access the namespace of a particular entity? Eg namespace_of(SomeClass)::function_in_that_namespace() .

No.

---

You'll have to find a different approach, such as wrapping myfunc in another function, that uses ADL to call myfunc by default, but can be overloaded. Or something similar.