Capturing-lambda-to-function-pointer cast

#pragma once

#include <type_traits>
#include <utility>

template <typename F>
struct lambda_traits : lambda_traits<decltype(&F::operator())> {};

template <typename F, typename R, typename... Args>
struct lambda_traits<R(F::*)(Args...)> {
    using ptr_t = std::add_pointer_t<R(Args...)>;

    static inline ptr_t to_fptr(F&& f) {
        static F fn = std::forward<F>(f);
        return [](Args... args) {
            return fn(std::forward<Args>(args)...);
        };
    }
};

template <typename F, typename R, typename... Args>
struct lambda_traits<R(F::*)(Args...) noexcept>
{
    using ptr_t = std::add_pointer_t<R(Args...)>;

    static inline auto to_fptr(F&& f) -> ptr_t {
        static F fn = std::forward<F>(f);
        return [](Args... args) {
            return fn(std::forward<Args>(args)...);
        };
    }
};

template <typename F, typename R, typename... Args>
struct lambda_traits<R(F::*)(Args...) const>
{
    using ptr_t = std::add_pointer_t<R(Args...)>;

    static inline auto to_fptr(F&& f) -> ptr_t {
        static F fn = std::forward<F>(f);
        return [](Args... args) {
            return fn(std::forward<Args>(args)...);
        };
    }
};

template <typename F, typename R, typename... Args>
struct lambda_traits<R(F::*)(Args...) const noexcept>
{
    using ptr_t = std::add_pointer_t<R(Args...)>;

    static inline auto to_fptr(F&& f) -> ptr_t {
        static F fn = std::forward<F>(f);
        return [](Args... args) {
            return fn(std::forward<Args>(args)...);
        };
    }
};

template <class F>
inline auto to_fptr(F&& f) {
    return lambda_traits<F>::to_fptr(std::forward<F>(f));
}