function_traits.h

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*
* This file contains private API, this might break at any time between releases.
* You have been warned!
*
* //Code based on a blogpost on https://functionalcpp.wordpress.com/2013/08/05/function-traits/
*
*/
#ifndef ZYPPNG_META_FUNCTION_TRAITS_H_INCLUDED
#define ZYPPNG_META_FUNCTION_TRAITS_H_INCLUDED
 
#include <cstddef>
#include <tuple>
#include <zypp-core/zyppng/meta/TypeTraits>
 
namespace zyppng {
 
template<class F, class = void >
struct function_traits;
 
template<class R, class... Args>
struct function_traits<R(Args...)>
{
    using return_type = R;
 
    static constexpr std::size_t arity = sizeof...(Args);
 
    template <std::size_t N>
    struct argument
    {
        static_assert(N >= 0 && N < arity, "error: invalid parameter index.");
        using type = typename std::tuple_element<N,std::tuple<Args...>>::type;
    };
};
 
// function pointer
template<class R, class... Args>
struct function_traits<R(*)(Args...)> : public function_traits<R(Args...)>
{ };
 
// function ref
template<class R, class... Args>
struct function_traits<R(&)(Args...)> : public function_traits<R(Args...)>
{ };
 
// member function pointer
template<class C, class R, class... Args>
struct function_traits<R(C::*)(Args...)> : public function_traits<R(C&,Args...)>
{};
 
// const member function pointer, this will match lambdas too
template<class C, class R, class... Args>
struct function_traits<R(C::*)(Args...) const>  : public function_traits<R(C&,Args...)>
{};
 
// member object pointer
template<class C, class R>
struct function_traits<R(C::*)> : public function_traits<R(C&)>
{};
 
template <typename T>
using has_call_operator = decltype (&T::operator());
 
//functor with one overload
template<class F>
struct function_traits<F, std::void_t<decltype (&F::operator())>> : public function_traits<decltype (&F::operator())>
{};
 
}
#endif