libcruft-util/functor.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <utility>


namespace cruft::functor {
    ///////////////////////////////////////////////////////////////////////////
    /// returns the value provided at construction time regardless of the
    /// arguments supplied in the call operator.
    template <typename ValueT>
    class constant {
    public:
        constant (const ValueT &_value):
            m_value (_value)
        { ; }


        template <typename ...Args>
        ValueT&
        operator() (Args&&...) noexcept
        { return m_value; }


        template <typename ...Args>
        const ValueT&
        operator() (Args&&...) const noexcept
        { return m_value; }


    private:
        ValueT m_value;
    };


    //-------------------------------------------------------------------------
    template <typename ValueT>
    constant (ValueT) -> constant<std::decay_t<ValueT>>;
};