Simplest way to determine return type of function

Question

Given a very simple, but lengthy function, such as:

int foo(int a, int b, int c, int d) {
    return 1;
}

// using ReturnTypeOfFoo = ???

W

Answer 1

Most simple and concise is probably:

template 
R return_type_of(R(*)(Args...));

using ReturnTypeOfFoo = decltype(return_type_of(foo));

Note that this won't work for function objects or pointers to member functions. Just functions, that aren't overloaded or templates, or noexcept.

But this can be extended to support all of those cases, if so desired, by adding more overloads of return_type_of.