Lambda std function witchcraft

lambda_witchcraft.cpp

#include <iostream>
#include <functional>

using namespace std;

template<typename T> struct memfn_ptr_to_fn_ptr { };
template<typename C, typename R, typename... A>
struct memfn_ptr_to_fn_ptr<R(C::*)(A...)> { using type = R(A...); };
template<typename C, typename R, typename... A>
struct memfn_ptr_to_fn_ptr<R(C::*)(A...) const> { using type = R(A...); };

template<typename L>
struct get_lambda_signature
{
    using type = typename memfn_ptr_to_fn_ptr<decltype(&L::operator())>::type;
};

template<typename L>
auto to_function(L lambda) -> std::function<typename get_lambda_signature<L>::type>
{
    return lambda;
}

template <typename T>
class TypePrinter;

int main(int argc, char** argv)
{
    int x = 2;
    auto f = [&x](int param) { return x*param;};
    auto f2 = [&x]() { return x;};
    auto f3 = [x](int param) mutable { return ++x*param;};
    auto f4 = [](int param) { return ++param;};
    auto f5 = [](int param) { ++param;};
    auto f6 = [](){};

    auto func = to_function(f);
    auto func2 = to_function(f2);
    auto func3 = to_function(f3);
    auto func4 = to_function(f4);
    auto func5 = to_function(f5);
    auto func6 = to_function(f6);

//    TypePrinter<decltype(func6)>();

    return 0;
}