utility.hh

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// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
// vi: set et ts=4 sw=4 sts=4:
//
// SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
// SPDX-License-Identifier: GPL-3.0-or-later
//
#ifndef DUMUX_COMMON_TYPETRAITS_UTILITY_HH
#define DUMUX_COMMON_TYPETRAITS_UTILITY_HH
 
#include <cstddef>
#include <utility>
 
namespace Dumux {
 
/*
 * \ingroup Typetraits
 * \brief create a variadic template from indexed types
 * \tparam V a variadic template that we want to create
 * \tparam T an indexed type (type that gets an index as template parameter)
 * \tparam U the list of indices
 */
template <template<typename... Args> class Variadic, template<std::size_t> class Indexed, class U>
struct makeFromIndexedType;
 
template <template<typename... Args> class Variadic, template<std::size_t> class Indexed, std::size_t... IndexSeq>
struct makeFromIndexedType<Variadic, Indexed, std::index_sequence<IndexSeq...>>
{
    using type = Variadic<Indexed<IndexSeq>...>;
};
 
namespace Detail {
    template <class Seq1, std::size_t offset, class Seq2> struct ConcatSeq;
 
    template <std::size_t ... Is1, std::size_t offset, std::size_t ... Is2>
    struct ConcatSeq<std::index_sequence<Is1...>, offset, std::index_sequence<Is2...>>
    {
        using type = std::index_sequence<Is1..., (offset + Is2)...>;
    };
}
 
/*
 * \ingroup Typetraits
 * \brief create an integer sequence from 0 to n-1, omitting one specific number e
 * \tparam n number of integers in complete sequence before omitting
 * \tparam e value of integer to be omitted
 *
 * example: makeIncompleteIntegerSequence<3, 1> = [0, 2]
 * example: makeIncompleteIntegerSequence<4, 4> = [0, 1, 2, 3]
 *
 * see https://stackoverflow.com/questions/27124920/compile-time-generate-integer-sequence-with-one-left-out for details
 */
template <std::size_t n, std::size_t e>
using makeIncompleteIntegerSequence =
        typename Detail::ConcatSeq<decltype(std::make_index_sequence<e>{}), e + 1, decltype(std::make_index_sequence<(n > e) ? (n - e - 1) : 0>{})>::type;
 
/*
 * \ingroup Typetraits
 * \brief add an offset to an index sequence
 * \tparam offset the offset
 * \tparam is the index sequence
 *
 * see https://stackoverflow.com/a/35625414
 */
template <std::size_t offset, std::size_t ... is>
constexpr std::index_sequence<(offset + is)...> addOffsetToIndexSequence(std::index_sequence<is...>)
{ return {}; }
 
/*
 * \ingroup Typetraits
 * \brief create an index sequence starting from an offset
 * \tparam offset the offset
 * \tparam n the length of the sequence
 *
 * example: makeIndexSequenceWithOffset<2, 3> = [2,3,4]
 *
 * see https://stackoverflow.com/a/35625414
 */
template <std::size_t offset, std::size_t n>
constexpr auto makeIndexSequenceWithOffset()
{
    return addOffsetToIndexSequence<offset>(std::make_index_sequence<n>{});
}
 
} // end namespace Dumux
 
#endif