meta.hpp

#ifndef GNR_META_HPP
# define GNR_META_HPP
# pragma once

#include <cstddef>

#include <type_traits>

namespace gnr
{

template <std::size_t I, typename A, typename ...B>
struct type_at : type_at<I - 1, B...>
{
};

template <typename A, typename ...B>
struct type_at<0, A, B...>
{
  using type = A;
};

template <typename A, typename ...B>
struct front
{
  using type = A;
};

template <typename ...A>
using front_t = typename front<A...>::type;

template <typename A, typename ...B>
struct back : back<B...>
{
};

template <typename A>
struct back<A>
{
  using type = A;
};

template <typename ...A>
using back_t = typename back<A...>::type;

template <class A, class ...B>
struct all_of : std::integral_constant<bool,
  A{} &&
  all_of<B...>{}
>
{
};

template <class A>
struct all_of<A> : std::integral_constant<bool, A{}>
{
};

template <class A, class ...B>
struct any_of : std::integral_constant<bool,
  A{} ||
  any_of<B...>{}
>
{
};

template <class A>
struct any_of<A> : std::integral_constant<bool, A{}>
{
};

}

#endif // GNR_META_HPP