Convert lambda to std::function

lambda_to_function.cpp

// g++ prog.cc -Wall -Wextra -O2 -march=native -std=gnu++1y 

#include <cxxabi.h>

#include <algorithm>
#include <functional>
#include <iostream>
#include <typeinfo>

namespace detail
{
    template <typename F>
    struct function_traits : public function_traits<decltype(&F::operator())> {};

    template <typename R, typename C, typename... Args>
    struct function_traits<R (C::*)(Args...) const>
    {
        using function_type = std::function<R (Args...)>;
    };
}

template <typename F>
using function_type_t = typename detail::function_traits<F>::function_type;

template <typename F>
function_type_t<F> to_function(F & lambda)
{
    return static_cast<function_type_t<F>>(lambda);
}

template <typename T>
std::string type_id(const T & t)
{
    int status = 0;
    char * tmp = abi::__cxa_demangle(typeid(t).name(), 0, 0, &status);
    std::string result(tmp);
    free(tmp);

    return std::move(result);
};

int main(int argc, char const *argv[])
{
    auto lambda = [argc, &argv]()
    {
        std::for_each(argv, argv + argc,
            [](const char * arg)
            {
                std::cout << arg << std::endl;
            });
    };
    
    // convert lambda to std::function
    auto f = to_function(lambda);

    std::cout << type_id(lambda) << std::endl;
    std::cout << type_id(f) << std::endl;
    
    // convert std::function to std::function
    to_function(f)();

    return 0;
}