any_objective_function.h

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/*
 * Copyright 2024 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 <functional>
#include <type_traits>
#include <utility>
 
#include "num_collect/base/concepts/invocable_as.h"
 
namespace num_collect::opt {

template <typename Signature>
class any_objective_function;

template <typename Value, typename Variable>
class any_objective_function<Value(Variable)> {
public:
    using variable_type = std::decay_t<Variable>;

    using value_type = std::decay_t<Value>;

    any_objective_function() = default;

    template <base::concepts::invocable_as<Value(Variable)> Function>
    any_objective_function(  // NOLINT(*-explicit-constructor,*-explicit-conversions)
        Function&& function)
        : function_(std::forward<Function>(function)) {}

    template <base::concepts::invocable_as<Value(Variable)> Function>
    auto operator=(  // NOLINT(*-explicit-constructor,*-explicit-conversions)
        Function&& function) -> any_objective_function& {
        function_ = std::forward<Function>(function);
        return *this;
    }

    void evaluate_on(const variable_type& variable) {
        value_ = function_(variable);
    }

    [[nodiscard]] auto value() const noexcept -> const value_type& {
        return value_;
    }
 
private:
    std::function<Value(Variable)> function_{};

    value_type value_{};
};
 
}  // namespace num_collect::opt