CppUtils/modules/Type/VariadicTemplate.mpp at master · MorganCaron/CppUtils · GitHub

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export module CppUtils.Type.VariadicTemplate;

import std;
import CppUtils.Type.Concept;

export namespace CppUtils::Type
{
	template<std::size_t I, class... Types>
	requires (I < sizeof...(Types))
	using NthType = Types...[I];

	template<class... Types>
	using FirstType = NthType<0, Types...>;

	template<class T, class... Types>
	requires IsOneOf<T, Types...>
	consteval auto getPosition() -> std::size_t
	{
		auto i = 0uz;
		static_cast<void>(((++i, std::same_as<T, Types>) or ...));
		return --i;
	}

	template<class T, class... Types>
	struct Unique: std::type_identity<T>
	{};

	template<template<class...> class Container, class... Types, class Candidate, class... NextCandidates>
	struct Unique<Container<Types...>, Candidate, NextCandidates...>:
		std::conditional_t<(std::is_same_v<Candidate, Types> or ...),
			Unique<Container<Types...>, NextCandidates...>,
			Unique<Container<Types..., Candidate>, NextCandidates...>>
	{};

	template<template<class...> class Container, class... Types>
	using UniqueType = typename Unique<Container<>, Types...>::type;

	template<class... Types>
	using UniqueVariant = UniqueType<std::variant, std::decay_t<Types>...>;

	template<class... Types>
	using UniqueTuple = UniqueType<std::tuple, Types...>;

	template<template<class> class Trait, class T, class... Types>
	struct Filter: std::type_identity<T>
	{};

	template<template<class> class Trait, template<class...> class Container, class... Types, class Candidate, class... NextCandidates>
	struct Filter<Trait, Container<Types...>, Candidate, NextCandidates...>:
		std::conditional_t<Trait<Candidate>::value,
			Filter<Trait, Container<Types..., Candidate>, NextCandidates...>,
			Filter<Trait, Container<Types...>, NextCandidates...>>
	{};

	template<template<class> class Trait, template<class...> class Container, class... Types>
	using FilterType = typename Filter<Trait, Container<>, Types...>::type;
}