pattern_collection.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) 2024-2026 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_PATTERN_COLLECTION_HPP
#define OPENKALMAN_PATTERN_COLLECTION_HPP

#include "collections/collections.hpp"
#include "sized_pattern.hpp"

namespace OpenKalman::patterns
{
#if not defined(__cpp_concepts) or __cpp_generic_lambdas < 201707L
  namespace detail
  {
    template<typename T, std::size_t...Ix>
    constexpr bool is_pattern_iter_impl(std::index_sequence<Ix...>)
    {
      return (... and sized_pattern<collections::collection_element_t<Ix, T>>);
    }


    template<typename T, typename = void>
    struct is_pattern_iter : std::false_type {};

    template<typename T>
    struct is_pattern_iter<T, std::enable_if_t<collections::uniformly_gettable<T>>>
      : std::bool_constant<is_pattern_iter_impl<T>(std::make_index_sequence<collections::size_of_v<T>>{})> {};


    template<typename T, typename = void>
    struct is_pattern_range : std::false_type {};

    template<typename T>
    struct is_pattern_range<T, std::enable_if_t<sized_pattern<stdex::ranges::range_value_t<T>>>>
      : std::true_type {};
  }
#endif


  template<typename T>
#if defined(__cpp_concepts) and __cpp_generic_lambdas >= 201707L
  concept pattern_collection =
    collections::collection<T> and
    ( ( std::ranges::random_access_range<T> and
        sized_pattern<std::ranges::range_value_t<T>>) or
      []<std::size_t...Ix>(std::index_sequence<Ix...>)
        { return (... and sized_pattern<collections::collection_element_t<Ix, T>>); }
        (std::make_index_sequence<collections::size_of<T>::value>{})
    );
#else
  constexpr bool pattern_collection =
    collections::collection<T> and
    ( ( stdex::ranges::random_access_range<T> and
        detail::is_pattern_range<T>::value) or
      detail::is_pattern_iter<T>::value
    );
#endif

}

#endif