gecko-dev/xpcom/base/nsIPtr.h

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/*
* The contents of this file are subject to the Netscape Public License
* Version 1.0 (the "NPL"); you may not use this file except in
* compliance with the NPL. You may obtain a copy of the NPL at
* http://www.mozilla.org/NPL/
*
* Software distributed under the NPL is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
* for the specific language governing rights and limitations under the
* NPL.
*
* The Initial Developer of this code under the NPL is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All Rights
* Reserved.
*/
#ifndef nsIPtr_h___
#define nsIPtr_h___
#include "nsISupports.h"
/*
* nsIPtr is an "auto-release pointer" class for nsISupports based interfaces
*
* It's intent is to be a "set and forget" pointer to help with managing
* active references to nsISupports bases objects.
*
* The pointer object ensures that the underlying pointer is always
* released whenever the value is changed or when the object leaves scope.
*
* Proper care needs to be taken when assigning pointers to a nsIPtr.
* When asigning from a C pointer (nsISupports*), the pointer presumes
* an active reference and subsumes it. When assigning from another nsIPtr,
* a new reference is established.
*
* There are 3 ways to assign a value to a nsIPtr.
* 1) Direct construction or assignment from a C pointer.
* 2) Direct construction or assignment form another nsIPtr.
* 3) Usage of an "out parameter" method.
* a) AssignRef() releases the underlying pointer and returns a reference to it.
* Useful for pointer reference out paramaters.
* b) AssignPtr() releases the underlying pointer and returns a pointer to it.
* c) Query() releases the underlying pointer and returns a (void**) pointer to it.
* Useful for calls to QueryInterface()
* 4) The SetAddRef() method. This is equivalent to an assignment followed by an AddRef().
*
* examples:
*
* class It {
* void NS_NewFoo(nsIFoo** aFoo);
* nsIFoo* GetFoo(void);
* void GetBar(nsIBar*& aBar);
* };
*
* nsIFooPtr foo = it->GetFoo();
* nsIBarPtr bar;
*
* it->NS_NewFoo(foo.AssignPtr());
* it->GetBar(bar.AssignRef());
* it->QueryInterface(kIFooIID, foo.Query());
* bar.SetAddRef(new Bar());
*
* Advantages:
* Set and forget. Once a pointer is assigned to a nsIPtr, it is impossible
* to forget to release it.
* Always pre-initialized. You can't forget to initialize the pointer.
*
* Disadvantages:
* Usage of this class doesn't eliminate the need to think about ref counts
* and assign values properly, AddRef'ing as needed.
* The nsIPtr doesn't typecast exactly like a C pointer. In order to achieve
* typecasting, it may be necessary to first cast to a C pointer of the
* underlying type.
*
*/
#define NS_DEF_PTR(cls) \
class cls##Ptr { \
public: \
cls##Ptr(void) : mPtr(0) {} \
cls##Ptr(const cls##Ptr& aCopy) : mPtr(aCopy.mPtr) \
{ NS_IF_ADDREF(mPtr); } \
cls##Ptr(cls* aInterface) : mPtr(aInterface) {} \
~cls##Ptr(void) { NS_IF_RELEASE(mPtr); } \
cls##Ptr& operator=(const cls##Ptr& aCopy) \
{ if(mPtr == aCopy.mPtr) return *this; \
NS_IF_ADDREF(aCopy.mPtr); \
NS_IF_RELEASE(mPtr); \
mPtr = aCopy.mPtr; return *this; } \
cls##Ptr& operator=(cls* aInterface) \
{ if(mPtr == aInterface) return *this; \
NS_IF_RELEASE(mPtr); mPtr = aInterface; \
return *this; } \
cls##Ptr& operator=(PRInt32 aInt) \
{ NS_IF_RELEASE(mPtr); \
return *this; } \
void SetAddRef(cls* aInterface) \
{ if(aInterface == mPtr) return; \
NS_IF_ADDREF(aInterface); \
NS_IF_RELEASE(mPtr); mPtr = aInterface; } \
cls* AddRef(void) { NS_ADDREF(mPtr); return mPtr; } \
cls* IfAddRef(void) \
{ NS_IF_ADDREF(mPtr); return mPtr; } \
cls*& AssignRef(void) \
{ NS_IF_RELEASE(mPtr); return mPtr; } \
cls** AssignPtr(void) \
{ NS_IF_RELEASE(mPtr); return &mPtr; } \
void** Query(void) \
{ NS_IF_RELEASE(mPtr); return (void**)&mPtr; } \
PRBool IsNull() const \
{ return PRBool(0 == mPtr); } \
PRBool IsNotNull() const \
{ return PRBool(0 != mPtr); } \
PRBool operator==(const cls##Ptr& aCopy) const \
{ return PRBool(mPtr == aCopy.mPtr); } \
PRBool operator==(cls* aInterface) const \
{ return PRBool(mPtr == aInterface); } \
PRBool operator!=(const cls##Ptr& aCopy) const \
{ return PRBool(mPtr != aCopy.mPtr); } \
PRBool operator!=(cls* aInterface) const \
{ return PRBool(mPtr != aInterface); } \
cls* operator->(void) { return mPtr; } \
cls& operator*(void) { return *mPtr; } \
operator cls*(void) { return mPtr; } \
const cls* operator->(void) const { return mPtr; } \
const cls& operator*(void) const { return *mPtr; } \
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operator const cls* (void) const { return mPtr; } \
private: \
void* operator new(size_t size) { return 0; } \
void operator delete(void* aPtr) {} \
cls* mPtr; \
public: \
friend inline PRBool operator==(const cls* aInterface, const cls##Ptr& aPtr) \
{ return PRBool(aInterface == aPtr.mPtr); } \
friend inline PRBool operator!=(const cls* aInterface, const cls##Ptr& aPtr) \
{ return PRBool(aInterface != aPtr.mPtr); } \
}
#endif // nsIPtr_h___