function_object_wrapper.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>
#include <utility>
 
namespace num_collect::opt {
 
template <typename Signature, typename Function>
class function_object_wrapper;
 
template <typename Value, typename Variable, typename Function>
class function_object_wrapper<Value(Variable), Function> {
public:
    using variable_type = std::decay_t<Variable>;
 
    using value_type = std::decay_t<Value>;
 
    using function_type = std::decay_t<Function>;
 
    explicit function_object_wrapper(function_type function)
        : function_(std::move(function)) {}
 
    void evaluate_on(const variable_type& variable) {
        value_ = function_(variable);
    }
 
    [[nodiscard]] auto value() const -> const value_type& { return value_; }
 
private:
    function_type function_;
 
    value_type value_{};
};
 
template <typename Signature, typename Function>
[[nodiscard]] inline auto make_function_object_wrapper(Function&& function)
    -> function_object_wrapper<Signature, Function> {
    return function_object_wrapper<Signature, Function>(
        std::forward<Function>(function));
}
 
}  // namespace num_collect::opt