Fold.h

/*
 *
 *    Copyright (c) 2021 Project CHIP Authors
 *
 *    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>

namespace chip {

/**
 * Apply the functor sequentially to the previous value and a subsequent element of the container.
 *
 * This provides a similar functionality to std::acumulate, but can be used in constexpr contexts.
 */
template <class Container, class Functor, class ValueType = typename Container::value_type>
constexpr ValueType Fold(const Container & container, ValueType initial, Functor functor)
{
    for (const auto & element : container)
    {
        initial = functor(initial, element);
    }

    return initial;
}

/**
 * Sum all elements of the container using "+" operator.
 */
template <class Container, class ValueType = typename Container::value_type>
constexpr ValueType Sum(const Container & container)
{
    return Fold(container, ValueType{}, std::plus<ValueType>{});
}

} // namespace chip