Member function call in decltype

Question

The following code:

struct A
{
    int f(int);
    auto g(int x) -> decltype(f(x));
};

Fails to compile with the error:

erro         


        

Answer 1

Seems to me that does not work because the decltype is outside of the method and A is at that moment an incomplete type (so you can't even do A().f(x)).

But you should not really need that. Outside of the declaration of A this will work as expected, in A you should know the return type of the function that you declared a few lines above. Or you could just write:

struct A {
    typedef int ret_type;
    ret_type f(int x);
    ret_type g(int x);
};

This even works with plain c++03.