#include <iostream>
#include <utility>
#include <typeinfo>
 
struct A{};
struct B{};
 
struct X
{
    double f(A&);
    int* f(B&);
};
 
double X::f(A&) { return 0; }
int* X::f(B&) { return 0; }
 
template<typename T, typename R = decltype(std::declval<X>().f(std::declval<T&>()))>
R ff(T& arg)
{
	std::cout << typeid(R).name() << std::endl;
    X x;
    R r = x.f(arg); // preferably if I can create local variables of type R here
    return r;
}
 
int main()
{
    A a; ff(a);
    B b; ff(b);
    return 0;
}

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