Weakable.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include "Assertions.h"
#include "RefCounted.h"
#include "RefPtr.h"

namespace AK {

template<typename T>
class Weakable;
template<typename T>
class WeakPtr;

template<typename T>
class WeakLink : public RefCounted<WeakLink<T>> {
    friend class Weakable<T>;

public:
    T* ptr() { return static_cast<T*>(m_ptr); }
    const T* ptr() const { return static_cast<const T*>(m_ptr); }

private:
    explicit WeakLink(T& weakable)
        : m_ptr(&weakable)
    {
    }
    T* m_ptr;
};

template<typename T>
class Weakable {
private:
    class Link;

public:
    WeakPtr<T> make_weak_ptr();

protected:
    Weakable() {}

    ~Weakable()
    {
#ifdef DEBUG
        m_being_destroyed = true;
#endif
        if (m_link)
            m_link->m_ptr = nullptr;
    }

private:
    RefPtr<WeakLink<T>> m_link;
#ifdef DEBUG
    bool m_being_destroyed { false };
#endif
};

}

using AK::Weakable;