size.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) 2025 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_VALUES_SIZE_HPP
#define OPENKALMAN_VALUES_SIZE_HPP

#include <type_traits>
#include "index.hpp"

namespace OpenKalman::values
{
  struct unbounded_size_t
  {
    friend constexpr bool operator==(unbounded_size_t, unbounded_size_t) noexcept { return true; }

#ifdef __cpp_concepts
    template<index T>
#else
    template<typename T, std::enable_if_t<index<T>, int> = 0>
#endif
    friend constexpr bool operator==(unbounded_size_t, const T&) noexcept { return false; }

#ifndef __cpp_lib_three_way_comparison
#ifdef __cpp_concepts
    template<index T>
#else
    template<typename T, std::enable_if_t<index<T>, int> = 0>
#endif
    friend constexpr bool operator==(const T&, unbounded_size_t) noexcept { return false; }
#endif
  };




  inline constexpr unbounded_size_t unbounded_size {};


#ifdef __cpp_concepts
  template<typename T>
  concept size =
#else
  template<typename T>
  constexpr bool size =
#endif
    index<T> or stdex::same_as<std::decay_t<T>, unbounded_size_t>;


}

#endif