c++11: How to write a wrapper function to make `std::function` objects

Question

I am trying to write a wrapper make_function, which like std::make_pair can create a std::function object out of suitable callable obj

Answer 1

In general you cannot solve it without the severe restriction that whatever you pass to make_function is only callable with exactly one signature.

What are you going to do with something like:

struct Generic
{
    void operator()() { /* ... */ }
    void operator()() const { /* ... */ }

    template
    T operator()(T&& t, Ts&&...) { /* ... */ }

    template
    T operator()(T&& t, Ts&&...) const { /* ... */ }
};

C++14 generic lambdas will have the same issue.

The signature in std::function is based on how you plan to call it and not on how you construct/assign it.

You cannot solve it for std::bind either, as that has indefinite arity:

void foo() { std::cout << "foo()" << std::endl; }
//...

auto f = std::bind(foo);
f();                 // writes "foo()"
f(1);                // writes "foo()"
f(1, 2, 3, 4, 5, 6); // writes "foo()"