How can I determine the return type of a C++11 member function

Question

I am trying to determine the return type of a various C++ member functions. I understand that decltype and std::declval can be used to do this, but I am having problems with the

Answer 1

I've tried various declarations such as decltype(std::declval(TestCBClass::testStaticMethod))

You don't have to use std::declval and pass actual arguments, not even their types, just to know what is the return type of a static/non-static member function. Instead, you can write your own trait to know what is the return type of a given function:

template 
struct return_type;
template 
struct return_type { using type = R; };
template 
struct return_type { using type = R; };
template 
struct return_type { using type = R; };
template 
struct return_type { using type = R; };
template 
struct return_type { using type = R; };
template 
using return_type_t = typename return_type::type;

...

TestCBClass t;

std::future> a =
        std::async(&TestCBClass::testCBArgRet, t, 1);

std::future> b =
        std::async(&TestCBClass::testCBEmpty, t);

std::future> c =
        std::async(&TestCBClass::testCBEmptyStatic);

DEMO