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

Comeau doesn't like auto as a top level return type, but the following compiles successfully:

template  R get_return_type(R (C::*)(A1));

struct A
{
    int f(int);
    decltype(get_return_type(&A::f)) g(int x);
};

Basically, you have to declare at least one additional construct that gets you the type you want. And use decltype directly.

EDIT: Incidentally, this works fine for diving into the return type of a member function as well:

template  R get_return_type(R (C::*)(A1));

struct B { int f(int); };

struct A
{
    int f(int);
    B h(int);

    decltype(get_return_type(&A::f)) g(int x);

    decltype(get_return_type(&A::h).f(0)) k(int x);
};

int main()
{
    return A().k(0);
}

Granted, it doesn't have the same convenience of auto f()-> ..., but at least it compiles.