CartesianProduct.hpp

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/* Copyright 2022 Benjamin Worpitz, Bernhard Manfred Gruber
 * SPDX-License-Identifier: MPL-2.0
 */
 
#pragma once
 
#include "alpaka/meta/Concatenate.hpp"
 
namespace alpaka::meta
{
    // This is based on code by Patrick Fromberg.
    // See
    // http://stackoverflow.com/questions/9122028/how-to-create-the-cartesian-product-of-a-type-list/19611856#19611856
    namespace detail
    {
        template<typename... Ts>
        struct CartesianProductImplHelper;
 
        // Stop condition.
        template<template<typename...> class TList, typename... Ts>
        struct CartesianProductImplHelper<TList<Ts...>>
        {
            using type = TList<Ts...>;
        };
 
        // Catches first empty tuple.
        template<template<typename...> class TList, typename... Ts>
        struct CartesianProductImplHelper<TList<TList<>>, Ts...>
        {
            using type = TList<>;
        };
 
        // Catches any empty tuple except first.
        template<template<typename...> class TList, typename... Ts, typename... Rests>
        struct CartesianProductImplHelper<TList<Ts...>, TList<>, Rests...>
        {
            using type = TList<>;
        };
 
        template<template<typename...> class TList, typename... X, typename H, typename... Rests>
        struct CartesianProductImplHelper<TList<X...>, TList<H>, Rests...>
        {
            using type1 = TList<Concatenate<X, TList<H>>...>;
            using type = typename CartesianProductImplHelper<type1, Rests...>::type;
        };
 
        template<
            template<typename...>
            class TList,
            typename... X,
            template<typename...>
            class Head,
            typename T,
            typename... Ts,
            typename... Rests>
        struct CartesianProductImplHelper<TList<X...>, Head<T, Ts...>, Rests...>
        {
            using type1 = TList<Concatenate<X, TList<T>>...>;
            using type2 = typename CartesianProductImplHelper<TList<X...>, TList<Ts...>>::type;
            using type3 = Concatenate<type1, type2>;
            using type = typename CartesianProductImplHelper<type3, Rests...>::type;
        };
 
        template<template<typename...> class TList, typename... Ts>
        struct CartesianProductImpl;
 
        // The base case for no input returns an empty sequence.
        template<template<typename...> class TList>
        struct CartesianProductImpl<TList>
        {
            using type = TList<>;
        };
 
        // R is the return type, Head<A...> is the first input list
        template<template<typename...> class TList, template<typename...> class Head, typename... Ts, typename... Tail>
        struct CartesianProductImpl<TList, Head<Ts...>, Tail...>
        {
            using type = typename detail::CartesianProductImplHelper<TList<TList<Ts>...>, Tail...>::type;
        };
    } // namespace detail
 
    template<template<typename...> class TList, typename... Ts>
    using CartesianProduct = typename detail::CartesianProductImpl<TList, Ts...>::type;
} // namespace alpaka::meta