empty_object.hpp

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/* This file is part of OpenKalman, a header-only C++ library for
 * Kalman filters and other recursive filters.
 *
 * Copyright (c) 2019-2023 Christopher Lee Ogden <ogden@gatech.edu>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#ifndef OPENKALMAN_EMPTY_OBJECT_HPP
#define OPENKALMAN_EMPTY_OBJECT_HPP


namespace OpenKalman
{
  namespace detail
  {
    template<typename T, Applicability b, std::size_t...Ix>
    constexpr bool has_0_dim(std::index_sequence<Ix...>)
    {
      return (dimension_size_of_index_is<T, Ix, 0, b> or ...);
    }
  } // namespace detail


  template<typename T, Applicability b = Applicability::guaranteed>
#ifdef __cpp_concepts
  concept empty_object =
#else
  constexpr bool empty_object =
#endif
    indexible<T> and (index_count_v<T> != dynamic_size or b != Applicability::guaranteed) and
    (index_count_v<T> == dynamic_size or detail::has_0_dim<T, b>(std::make_index_sequence<index_count_v<T>>{}));


} // namespace OpenKalman

#endif //OPENKALMAN_EMPTY_OBJECT_HPP