libcruft-util/scoped.hpp

/*
 * 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.
 *
 * Copyright 2012-2018, Danny Robson <danny@nerdcruft.net>
 */

#pragma once


namespace util::scoped {
    ///////////////////////////////////////////////////////////////////////////
    /// restores a referenced target variable to its original value at
    /// destruction time. the type must be copyable.
    template <typename ValueT>
    class restore {
    public:
        explicit restore (ValueT &_target):
            m_target (_target),
            m_value  (_target)
        { ; }

        ~restore ()
        {
            m_target = m_value;
        }

    private:
        ValueT &m_target;
        ValueT const m_value;
    };


    //-------------------------------------------------------------------------
    template <typename ValueT>
    restore (ValueT&) -> restore<ValueT>;


    ///////////////////////////////////////////////////////////////////////////
    /// increments the referenced variable at construction time, and
    /// decrements at destruction time.
    template <typename ValueT>
    class increment {
    public:
        explicit increment (ValueT &_target):
            m_target (_target)
        {
            ++m_target;
        }


        ~increment ()
        {
            --m_target;
        }

    private:
        ValueT &m_target;
    };


    //-------------------------------------------------------------------------
    template <typename ValueT>
    increment (ValueT&) -> increment<ValueT>;


    ///////////////////////////////////////////////////////////////////////////
    /// calls a function with the supplied arguments at destruction time
    template <typename FuncT, typename ...Args>
    class function {
    public:
        explicit function (FuncT &&_function, Args&& ..._args)
        noexcept (
            std::is_nothrow_move_constructible_v<FuncT> &&
            std::is_nothrow_move_constructible_v<std::tuple<Args...>>
        ):
            m_function (std::move (_function)),
            m_args (std::forward<Args> (_args)...)
        { ; }

        function (function&&);
        function (const function&);

        ~function ()
        {
            if (m_enabled)
                std::apply (std::move (m_function), std::move (m_args));
        }

        void disable (void) { m_enabled = false; }

    private:
        bool m_enabled = true;
        FuncT m_function;
        std::tuple<Args...> m_args;
    };


    //-------------------------------------------------------------------------
    template <typename FuncT, typename ...Args>
    function (FuncT &&, Args&&...) -> function<FuncT&&,Args&&...>;
};