/*

 * Copyright (C) 2009 Apple Inc. 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 APPLE INC. AND ITS 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 APPLE INC. OR ITS 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.

 */

#ifndef WeakGCPtr_h

#define WeakGCPtr_h

#include "Collector.h"

#include <wtf/Noncopyable.h>

namespace JSC {

// A smart pointer whose get() function returns 0 for cells awaiting destruction.

template <typename T> class WeakGCPtr : Noncopyable {

public:

    WeakGCPtr() : m_ptr(0) { }

    WeakGCPtr(T* ptr) { assign(ptr); }

    T* get() const

    {

        if (!m_ptr || !Heap::isCellMarked(m_ptr))

            return 0;

        return m_ptr;

    }

    bool clear(JSCell* ptr)

    {

        if (ptr == m_ptr) {

            m_ptr = 0;

            return true;

        }

        return false;

    }

    T& operator*() const { return *get(); }

    T* operator->() const { return get(); }

    bool operator!() const { return !get(); }

    // This conversion operator allows implicit conversion to bool but not to other integer types.

#if COMPILER(WINSCW)

    operator bool() const { return m_ptr; }

#else

    typedef T* WeakGCPtr::*UnspecifiedBoolType;

    operator UnspecifiedBoolType() const { return get() ? &WeakGCPtr::m_ptr : 0; }

#endif

    WeakGCPtr& operator=(T*);

#if !ASSERT_DISABLED

    bool hasDeadObject() const { return !!m_ptr; }

#endif

private:

    void assign(T* ptr)

    {

        ASSERT(ptr);

        Heap::markCell(ptr);

        m_ptr = ptr;

    }

    T* m_ptr;

};

template <typename T> inline WeakGCPtr<T>& WeakGCPtr<T>::operator=(T* optr)

{

    assign(optr);

    return *this;

}

template <typename T, typename U> inline bool operator==(const WeakGCPtr<T>& a, const WeakGCPtr<U>& b)

{ 

    return a.get() == b.get(); 

}

template <typename T, typename U> inline bool operator==(const WeakGCPtr<T>& a, U* b)

{ 

    return a.get() == b; 

}

template <typename T, typename U> inline bool operator==(T* a, const WeakGCPtr<U>& b) 

{

    return a == b.get(); 

}

template <typename T, typename U> inline bool operator!=(const WeakGCPtr<T>& a, const WeakGCPtr<U>& b)

{ 

    return a.get() != b.get(); 

}

template <typename T, typename U> inline bool operator!=(const WeakGCPtr<T>& a, U* b)

{

    return a.get() != b; 

}

template <typename T, typename U> inline bool operator!=(T* a, const WeakGCPtr<U>& b)

{ 

    return a != b.get(); 

}

template <typename T, typename U> inline WeakGCPtr<T> static_pointer_cast(const WeakGCPtr<U>& p)

{ 

    return WeakGCPtr<T>(static_cast<T*>(p.get())); 

}

template <typename T, typename U> inline WeakGCPtr<T> const_pointer_cast(const WeakGCPtr<U>& p)

{ 

    return WeakGCPtr<T>(const_cast<T*>(p.get())); 

}

template <typename T> inline T* getPtr(const WeakGCPtr<T>& p)

{

    return p.get();

}

} // namespace JSC

#endif // WeakGCPtr_h