formula.h

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/*
 * Copyright 2021 MusicScience37 (Kenta Kabashima)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once
 
#include <type_traits>  // IWYU pragma: keep
#include <utility>
 
#include "num_collect/base/concepts/const_reference_of.h"
#include "num_collect/base/concepts/decayed_to.h"
#include "num_collect/base/concepts/reference_of.h"
#include "num_collect/base/index_type.h"
#include "num_collect/logging/log_tag_view.h"
#include "num_collect/ode/concepts/problem.h"
 
namespace num_collect::ode::concepts {

template <typename T>
concept formula = requires(T& obj, const T& const_obj) {
    typename T::problem_type;
    typename T::variable_type;
    typename T::scalar_type;
 
    requires problem<typename T::problem_type>;
    requires std::is_same_v<typename T::variable_type,
        typename T::problem_type::variable_type>;
    requires std::is_same_v<typename T::scalar_type,
        typename T::problem_type::scalar_type>;
 
    { T::stages } -> base::concepts::decayed_to<index_type>;
    { T::order } -> base::concepts::decayed_to<index_type>;
    { T::log_tag } -> base::concepts::decayed_to<logging::log_tag_view>;
 
    { T(std::declval<typename T::problem_type>()) };
 
    {
        obj.step(std::declval<typename T::scalar_type>() /*time*/,
            std::declval<typename T::scalar_type>() /*step_size*/,
            std::declval<typename T::variable_type>() /*current*/,
            std::declval<typename T::variable_type&>() /*estimate*/)
    };
 
    { obj.problem() } -> base::concepts::reference_of<typename T::problem_type>;
    {
        const_obj.problem()
    } -> base::concepts::const_reference_of<typename T::problem_type>;
};
 
}  // namespace num_collect::ode::concepts