Question

Given a C++11 function:

X f(A, B, C);

Is there anyway from within this function:

template<typename T>
void g(T t)
{
    ...
}

Called as follows:

g(f);

to determine:

• the number of parameters of f
• the type of parameter i of f
• the return type of f

…

template<typename F>
void g(F f)
{
    constexpr size_t n = num_params<F>::n; // 3
    return_type<F>::type x; // X
    tuple<param_types<F>::type...> a; // tuple<A, B, C>
}

?

Answer 1

Sure:

template <typename R, typename ...Args>
void g(R(&f)(Args...))
{
    typedef R return_type;
    unsigned int const n_args = sizeof...(Args);

    // ...
}

Usage:

int foo(char, bool);

g(foo);