templates.hpp

#pragma once


namespace fowl{
namespace templates{


	// index<idx, TS...> returns the type at index idx
	template<std::size_t idx, typename... txs>
	struct index;

	template<std::size_t idx, typename tx, typename... txs>
	struct index<idx, tx, txs...>
	{
		using type = typename index<idx-1, txs...>::type;
	};
	template<typename tx, typename... txs>
	struct index<0, tx, txs...>
	{
		using type = tx;
	};

	template<
		template<typename...>typename tpl,
		typename... ts >
	using apply = tpl< ts... >;

	template<
		template<typename...> typename tpl,
		template<typename...> typename out,
		typename... ts >
	using map = out< apply< tpl, ts >... >;

	template< typename... Ts>
	struct pack
	{
		template< typename... Ys>
		using append = pack<Ts..., Ys...>;

		template< typename... Ys>
		using prepend = pack<Ys..., Ts...>;

		template< template<typename...> typename tpl>
		using apply = fowl::templates::apply< tpl, Ts... >;

		template< template<typename...> typename tpl>
		using map = typename fowl::templates:: map< tpl, fowl::templates::pack, Ts...>;

		template< std::size_t idx>
		using at = typename fowl::templates:: index< idx, Ts...>::type;

		static constexpr auto size = sizeof...(Ts);

	};

}
}