make_constant.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) 2022-2026 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_MAKE_CONSTANT_HPP
#define OPENKALMAN_MAKE_CONSTANT_HPP

#include "linear-algebra/concepts/constant_object.hpp"
#include "linear-algebra/functions/attach_patterns.hpp"
#include "linear-algebra/interfaces/stl/constant_mdspan_policies.hpp"

namespace OpenKalman
{
#ifdef __cpp_concepts
  template<values::value C, patterns::pattern_collection P> requires values::fixed<collections::size_of<P>>
  constexpr constant_object auto
#else
  template<typename C, typename P, std::enable_if_t<
    values::value<C> and
    patterns::pattern_collection<P> and
    values::fixed<collections::size_of<P>>, int> = 0>
  constexpr auto
#endif
  make_constant(C c, P&& p)
  {
    decltype(auto) extents = patterns::to_extents(std::forward<P>(p));
    typename interface::layout_constant::mapping<std::decay_t<decltype(extents)>> mapping(extents);
    interface::constant_accessor<C> accessor;
    auto m = stdex::mdspan {std::move(c), mapping, accessor};
    return attach_patterns(std::move(m), std::forward<P>(p));
  }


#ifdef __cpp_concepts
  template<values::value C, patterns::pattern...Ps>
  constexpr constant_object auto
#else
  template<typename C, typename...Ps, std::enable_if_t<values::value<C> and (... and patterns::pattern<Ps>), int> = 0>
  constexpr auto
#endif
  make_constant(C c, Ps&&...ps)
  {
    return make_constant(std::move(c), std::tuple{std::forward<Ps>(ps)...});
  }


#ifdef __cpp_concepts
  template<patterns::pattern_collection P, values::value C> requires
    std::default_initializable<P> and
    values::fixed<collections::size_of<P>>
  constexpr constant_object auto
#else
  template<typename P, typename C, std::enable_if_t<
    patterns::pattern_collection<P> and
    values::value<C> and
    values::fixed<collections::size_of<P>>, int> = 0>
  constexpr auto
#endif
  make_constant(C c)
  {
    return make_constant(std::move(c), P{});
  }


}

#endif