invocable_on_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) 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_INVOCABLE_ON_COLLECTION_HPP
#define OPENKALMAN_INVOCABLE_ON_COLLECTION_HPP

#ifdef __cpp_lib_ranges
#include <ranges>
#else
#include "basics/compatibility/ranges.hpp"
#endif
#include "tuple_like.hpp"

namespace OpenKalman::collections
{
  namespace detail
  {
#if not defined(__cpp_lib_ranges) or __cpp_generic_lambdas < 201707L
    template<typename R, typename F, typename = void, typename...Args>
    struct is_invocable_on_range : std::false_type {};

    template<typename R, typename F, typename...Args>
    struct is_invocable_on_range<R, F, std::enable_if_t<ranges::range<R>>, Args...>
      : std::bool_constant<std::is_invocable_v<F, ranges::range_value_t<R>, Args...>> {};


    template<typename Tup, typename = void>
    struct is_invocable_on_tuple_sequence { using type = std::index_sequence<>; };

    template<typename Tup>
    struct is_invocable_on_tuple_sequence<Tup, std::enable_if_t<tuple_like<Tup>>>
    { using type = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tup>>>; };


    template<typename Tup, typename F, typename Seq, typename...Args>
    struct is_invocable_on_tuple : std::false_type {};

    template<typename Tup, typename F, std::size_t...Ix, typename...Args>
    struct is_invocable_on_tuple<Tup, F, std::index_sequence<Ix...>, Args...>
      : std::bool_constant<(... and std::is_invocable_v<F&, std::tuple_element_t<Ix, Tup>, Args...>)> {};
#endif

  } // namespace detail


  template<typename F, typename C, typename...Args>
#if defined(__cpp_lib_ranges) and __cpp_generic_lambdas >= 201707L
  concept invocable_on_collection = collection<C> and
    (not std::ranges::range<C> or std::regular_invocable<F, std::ranges::range_value_t<C>, Args&&...>) and
    (not tuple_like<C> or
      []<std::size_t...i>(std::index_sequence<i...>) {
        return (... and std::regular_invocable<F&, std::tuple_element_t<i, C>, Args&&...>);
      } (std::make_index_sequence<size_of_v<C>>{}));
#else
  constexpr bool invocable_on_collection =
    (not ranges::range<C> or detail::is_invocable_on_range<C, F, void, Args&&...>::value) and
    (not tuple_like<C> or detail::is_invocable_on_tuple<C, F, typename detail::is_invocable_on_tuple_sequence<C>::type, Args&&...>::value);
#endif


} // namespace OpenKalman::collections

#endif //OPENKALMAN_INVOCABLE_ON_COLLECTION_HPP