conditional_list.hpp

/*********************************************************************
 *
 * Linear Arrangement Library - A library that implements a collection
 * algorithms for linear arrangments of graphs.
 *
 * Copyright (C) 2019 - 2023
 *
 * This file is part of Linear Arrangement Library. The full code is available
 * at:
 *      https://github.com/LAL-project/linear-arrangement-library.git
 *
 * Linear Arrangement Library is free software: you can redistribute it
 * and/or modify it under the terms of the GNU Affero General Public License
 * as published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * Linear Arrangement Library is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with Linear Arrangement Library.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Contact:
 *
 *     Lluís Alemany Puig (lalemany@cs.upc.edu)
 *         LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *         Webpage: https://cqllab.upc.edu/people/lalemany/
 *
 *     Ramon Ferrer i Cancho (rferrericancho@cs.upc.edu)
 *         LARCA (Laboratory for Relational Algorithmics, Complexity and Learning)
 *         CQL (Complexity and Quantitative Linguistics Lab)
 *         Office S124, Omega building
 *         Jordi Girona St 1-3, Campus Nord UPC, 08034 Barcelona.   CATALONIA, SPAIN
 *         Webpage: https://cqllab.upc.edu/people/rferrericancho/
 *
 ********************************************************************/
 
#pragma once
 
// lal includes
#include <lal/detail/type_traits/ith_type.hpp>
#include <lal/detail/type_traits/bool_sequence.hpp>
#include <lal/detail/type_traits/type_sequence.hpp>
 
namespace lal {
namespace detail {
 
template <std::size_t ith_idx, typename... Ts>
struct ith_type<ith_idx, type_sequence<Ts...>> : ith_type<ith_idx, Ts...>
{ };
 
template <typename bool_seq, typename type_seq>
struct conditional_list {
    using type =
        std::conditional_t<
            bool_seq::num_true == 0,
            std::nullptr_t,
            ith_type_t<bool_seq::index_true, type_seq>
        >;
};
 
template <typename bool_seq, typename type_seq>
using conditional_list_t = typename conditional_list<bool_seq, type_seq>::type;
 
 
static_assert(
    std::is_same_v<
        conditional_list_t<
            bool_sequence<false, false, true,   false>,
            type_sequence<int,   float, double, char>
        >,
        double
    >
);
static_assert(
    std::is_same_v<
        conditional_list_t<
            bool_sequence<false, false, false,  false>,
            type_sequence<int,   float, double, char>
        >,
        std::nullptr_t
    >
);
static_assert(
    std::is_same_v<
        conditional_list_t<
            bool_sequence<false, false, false,  true>,
            type_sequence<int,   float, double, char>
        >,
        char
    >
);
 
} // -- namespace detail
} // -- namespace lal