weakptr.h

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/*
**  ClanLib SDK
**  Copyright (c) 1997-2005 The ClanLib Team
**
**  This software is provided 'as-is', without any express or implied
**  warranty.  In no event will the authors be held liable for any damages
**  arising from the use of this software.
**
**  Permission is granted to anyone to use this software for any purpose,
**  including commercial applications, and to alter it and redistribute it
**  freely, subject to the following restrictions:
**
**  1. The origin of this software must not be misrepresented; you must not
**     claim that you wrote the original software. If you use this software
**     in a product, an acknowledgment in the product documentation would be
**     appreciated but is not required.
**  2. Altered source versions must be plainly marked as such, and must not be
**     misrepresented as being the original software.
**  3. This notice may not be removed or altered from any source distribution.
**
**  Note: Some of the libraries ClanLib link to may have additional
**  requirements or restrictions.
**
**  File Author(s):
**
**    Magnus Norddahl
*/


#ifndef header_weakptr
#define header_weakptr

#include "sharedptr.h"

//: Weak pointer class (pointer to a CL_SharedPtr object that dont increase reference count).
//- !group=Core/System!
//- !header=core.h!
//- <p>Use CL_WeakPtr when you want to have a pointer that is reference counted by CL_SharedPtr
//- but want a pointer that dont increase the reference count.</p>
//- <p>The purpose of CL_WeakPtr is to avoid circular loop issues. By using CL_WeakPtr you
//- can construct new CL_SharedPtr'ed objects based on the weak pointer.</p>
template <typename T, typename U = T>
class CL_WeakPtr
{
public:
        CL_WeakPtr() : impl(0) { return; }

        CL_WeakPtr(CL_SharedPtr<T, U> &other) : impl(other.get_impl()) { return; }

public:
        //: Returns true if this CL_SharedPtr is not dereferencable.
        bool is_null() const { return impl ? (impl->ptr == 0) : true; }

        //: Returns number of references (including this one) to the data cache.
        //- <p> Returns 0 if this pointer is null. </p>
        int get_ref_count() const { if (impl == 0) return 0; return impl->ref_count; }
        
        //: Gives access to the pointer itself.
        //- <p> Be careful not to keep the returned pointer around after doing any
        //- non-const operations on the CL_LazyCopyPtr; it could be invalid
        //- after that.</p>
        U* get() { return (U*) ((impl != 0) ? impl->ptr : 0); }

        const U* get() const { return (const U*) ((impl != 0) ? impl->ptr : 0); }

        //: Returns the pointer.
        operator U*() { return get(); }

        //: Returns the pointer.
        operator const U*() const { return get(); }

        //: Returns the pointer as a shared ptr.
        operator CL_SharedPtr<T, U>() const { return CL_SharedPtr<T, U>(impl); }

        //: Dereferencing operator.
        U& operator*() { return *((U*) impl->ptr); }

        U const& operator*() const { return *((const U*) impl->ptr); }
        
        //: Indirect member access operator.
        U* operator->() { return (U*) impl->ptr; }

        U const* operator->() const { return (const U*) impl->ptr; }

        //: Pointer equality check operator.
        //- <p> This will return true if the CL_SharedPtrs point to the same data. It doesn't
        //- check the data itself for equality. </p>
        bool operator==(const T* other) const { return other == ((impl != 0) ? impl->ptr : 0); }

        bool operator==(const CL_SharedPtr<T, U>& other) const { return other.impl == impl; }

        //: Copy assignment operator.
        CL_WeakPtr<T, U>& operator=(const CL_WeakPtr<T, U>& other)
        {
                impl = other.impl;
                return *this;
        }

private:
        CL_SharedPtr_Generic<T> *impl;
};

#endif

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