зеркало из https://github.com/mozilla/gecko-dev.git
669 строки
19 KiB
C++
669 строки
19 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/*
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* The contents of this file are subject to the Netscape Public License
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* Version 1.0 (the "NPL"); you may not use this file except in
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* compliance with the NPL. You may obtain a copy of the NPL at
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* http://www.mozilla.org/NPL/
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*
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* Software distributed under the NPL is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
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* for the specific language governing rights and limitations under the
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* NPL.
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*
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* The Initial Developer of this code under the NPL is Netscape
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* Communications Corporation. Portions created by Netscape are
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* Copyright (C) 1998 Netscape Communications Corporation. All Rights
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* Reserved.
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*/
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#ifndef nsCOMPtr_h___
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#define nsCOMPtr_h___
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// Wrapping includes can speed up compiles (see "Large Scale C++ Software Design")
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#ifndef nsDebug_h___
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#include "nsDebug.h"
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// for |NS_PRECONDITION|
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#endif
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#ifndef nsISupports_h___
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#include "nsISupports.h"
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// for |nsresult|, |NS_ADDREF|, et al
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#endif
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/*
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TO DO...
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+ make alternative function for |getter_AddRefs| (or something)
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+ make constructor for |nsQueryInterface| explicit (suddenly construct/assign from raw pointer becomes illegal)
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+ Improve internal documentation
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+ mention *&
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+ alternatives for comparison
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+ do_QueryInterface
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*/
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/* USER MANUAL
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See also:
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<http://www.meer.net/ScottCollins/doc/nsCOMPtr.html>, or
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<http://www.mozilla.org/projects/xpcom/nsCOMPtr.html>
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What is |nsCOMPtr|?
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|nsCOMPtr| is a `smart-pointer'. It is a template class that acts, syntactically,
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just like an ordinary pointer in C or C++, i.e., you can apply |*| or |->| to it to
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`get to' what it points at. |nsCOMPtr| is smart in that, unlike a raw COM
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interface pointer, |nsCOMPtr| manages |AddRef|, |Release|, and |QueryInterface|
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_for_ you.
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For instance, here is a typical snippet of code (at its most compact) where you assign
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a COM interface pointer into a member variable:
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NS_IF_RELEASE(mFoop); // If I have one already, I must release it before over-writing it.
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if ( mFooP = aPtr ) // Now it's safe to assign it in, and, if it's not NULL
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mFooP->AddRef(); // I must |AddRef| it, since I'll be holding on to it.
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If our member variable |mFooP| were a |nsCOMPtr|, however, the snippet above
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would look like this:
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mFoop = aPtr; // Note: automatically |Release|s the old and |AddRef|s the new
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|nsCOMPtr| helps you write code that is leak-proof, exception safe, and significantly
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less verbose than you would with raw COM interface pointers. With |nsCOMPtr|, you
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may never have to call |AddRef|, |Release|, or |QueryInterface| by hand.
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You still have to understand COM. You still have to know which functions return
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interface pointers that have already been |AddRef|ed and which don't. You still
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have to ensure your program logic doesn't produce circularly referencing garbage.
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|nsCOMPtr| is not a panacea. It is, however, helpful, easy to use, well-tested,
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and polite. It doesn't require that a function author cooperate with you, nor does
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your use force others to use it.
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Where should I use |nsCOMPtr|?
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...
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Where _shouldn't_ I use |nsCOMPtr|?
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In public interfaces... [[others]]
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How does a |nsCOMPtr| differ from a raw pointer?
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A |nsCOMPtr| differs, syntactically, from a raw COM interface pointer in three
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ways:
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+ It's declared differently, e.g.,
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// instead of saying // you say
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IFoo* fooP; nsCOMPtr<IFoo> fooP;
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+ You can't call |AddRef| or |Release| through it,
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fooP->AddRef(); // OK fooP->AddRef(); // Error: no permission
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fooP->Release(); // OK fooP->Release(); // Error: no permission
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+ You can't just apply an |&| to it to pass it to the typical `getter' function
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AcquireFoo(&fooP); AcquireFoo( getter_AddRefs(fooP) );
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GetFoo(&fooP); GetFoo( getter_doesnt_AddRef(fooP) );
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How do I use |nsCOMPtr|?
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Typically, you can use a |nsCOMPtr| exactly as you would a standard COM
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interface pointer:
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IFoo* fooP; nsCOMPtr<IFoo> fooP;
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// ... // ...
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fooP->SomeFunction(x, y, z); fooP->SomeFunction(x, y, z);
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AnotherFunction(fooP); AnotherFunction(fooP);
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if ( fooP ) if ( fooP )
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// ... // ...
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if ( fooP == barP ) if ( fooP == barP )
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// ... // ...
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There are some differences, though. In particular, you can't call |AddRef| or |Release|
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through a |nsCOMPtr| directly, nor would you need to. |AddRef| is called for you
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whenever you assign a COM interface pointer _into_ a |nsCOMPtr|. |Release| is
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called on the old value, and also when the |nsCOMPtr| goes out of scope. Trying
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to call |AddRef| or |Release| yourself will generate a compile-time error.
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fooP->AddRef(); // fooP->AddRef(); // ERROR: no permission
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fooP->Release(); // fooP->Release(); // ERROR: no permission
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The final difference is that a bare |nsCOMPtr| (or rather a pointer to it) can't
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be supplied as an argument to a function that `fills in' a COM interface pointer.
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Rather it must be wrapped with a utility call that says whether the function calls
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|AddRef| before returning, e.g.,
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...->QueryInterface(riid, &fooP) ...->QueryInterface(riid, getter_AddRefs(fooP))
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LookupFoo(&fooP); LookupFoo( getter_doesnt_AddRef(fooP) );
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Don't worry. It's a compile-time error if you forget to wrap it.
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Compare the raw-pointer way...
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IFoo* foo = 0;
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nsresult status = CreateIFoo(&foo);
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if ( NS_SUCCEEDED(status) )
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{
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IBar* bar = 0;
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if ( NS_SUCCEEDED(status = foo->QueryInterface(riid, &bar)) )
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{
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IFooBar* foobar = 0;
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if ( NS_SUCCEEDED(status = CreateIFooBar(foo, bar, &foobar)) )
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{
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foobar->DoTheReallyHardThing();
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foobar->Release();
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}
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bar->Release();
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}
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foo->Release();
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}
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To the smart-pointer way...
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nsCOMPtr<IFoo> fooP;
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nsresult status = CreateIFoo( getter_AddRefs(fooP) );
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if ( NS_SUCCEEDED(status) )
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if ( nsCOMPtr<IBar> barP( fooP ) )
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{
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nsCOMPtr<IFooBar> fooBarP;
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if ( NS_SUCCEEDED(status = CreateIFooBar(fooP, barP, getter_AddRefs(fooBarP))) )
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fooBarP->DoTheReallyHardThing();
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}
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Is there an easy way to convert my current code?
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...
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What do I have to beware of?
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VC++ < 6.0 _can't_ handle the following situation
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class nsIFoo; // forward declare some class
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// ...
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nsCOMPtr<nsIFoo> bar; // ERROR: incomplete type nsIFoo, etc.
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Instead, you must make sure that you actually defined the underlying interface class, e.g.,
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#include "nsIFoo.h" // fully defines |class nsIFoo|
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// ...
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nsCOMPtr<nsIFoo> bar; // no problem
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Why is this? It's because VC++ tries to instantiate every member of the template
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as soon as it sees the template declarations. Bad compiler. No cookie!
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[[Thanks to mjudge, waterson, and pinkerton on this one.]]
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Why does |getter_AddRefs| have such a funny name? I.e., why doesn't it follow our
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naming conventions?
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|getter_AddRefs| and |getter_doesnt_AddRef| use underscores for the same
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reason our special macros do, quoting from our coding conventions "...to make them
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stick out like a sore thumb". Note also that since |AddRef| is one word,
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|getter_AddRefs| and |getter_doesnt_AddRef| couldn't have the right spacing if only inter-
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caps were used.
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*/
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/*
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WARNING:
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This file defines several macros for internal use only. These macros begin with the
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prefix |NSCAP_|. Do not use these macros in your own code. They are for internal use
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only for cross-platform compatibility, and are subject to change without notice.
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*/
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/*
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Set up some |#define|s to turn off a couple of troublesome C++ features.
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Interestingly, none of the compilers barf on template stuff.
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Ideally, we would want declarations like these in a configuration file
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that everybody would get. Deciding exactly how to do that should
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be part of the process of moving from experimental to production.
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Update: ramiro is working on getting these into the configuration system.
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*/
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#if defined(__GNUG__) && (__GNUC_MINOR__ <= 90) && !defined(SOLARIS)
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#define NSCAP_NO_MEMBER_USING_DECLARATIONS
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#if (defined(LINUX) || defined(__bsdi__)) && (__GNUC_MINOR__ <= 7)
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#define NSCAP_NEED_UNUSED_VIRTUAL_IMPLEMENTATIONS
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#endif
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#endif
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#if defined(SOLARIS) && !defined(__GNUG__)
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#define NSCAP_NO_BOOL
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#define NSCAP_NO_EXPLICIT
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#define NSCAP_NO_NEW_CASTS
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#define NSCAP_NO_MEMBER_USING_DECLARATIONS
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#endif
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#if defined(_MSC_VER) && (_MSC_VER<1100)
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#define NSCAP_NO_EXPLICIT
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#define NSCAP_NO_BOOL
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#endif
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#if defined(IRIX)
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#define NSCAP_NO_MEMBER_USING_DECLARATIONS
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#define NSCAP_NO_EXPLICIT
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#define NSCAP_NO_NEW_CASTS
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#define NSCAP_NO_BOOL
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#endif
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#ifdef NSCAP_NO_EXPLICIT
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#define explicit
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#endif
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#ifndef NSCAP_NO_NEW_CASTS
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#define NSCAP_REINTERPRET_CAST(T,x) reinterpret_cast<T>(x)
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#else
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#define NSCAP_REINTERPRET_CAST(T,x) ((T)(x))
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#endif
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#ifndef NSCAP_NO_BOOL
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typedef bool NSCAP_BOOL;
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#else
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typedef PRBool NSCAP_BOOL;
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#endif
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#ifdef NSCAP_FEATURE_DEBUG_MACROS
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#define NSCAP_ADDREF(ptr) NS_ADDREF(ptr)
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#define NSCAP_RELEASE(ptr) NS_RELEASE(ptr)
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#else
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#define NSCAP_ADDREF(ptr) (ptr)->AddRef()
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#define NSCAP_RELEASE(ptr) (ptr)->Release()
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#endif
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/*
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WARNING:
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VC++4.2 is very picky. To compile under VC++4.2, the classes must be defined
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in an order that satisfies:
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nsDerivedSafe < nsCOMPtr
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nsDontAddRef < nsCOMPtr
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nsCOMPtr < nsGetterAddRefs
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The other compilers probably won't complain, so please don't reorder these
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classes, on pain of breaking 4.2 compatibility.
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*/
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template <class T>
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class nsDerivedSafe : public T
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/*
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No client should ever see or have to type the name of this class. It is the
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artifact that makes it a compile-time error to call |AddRef| and |Release|
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on a |nsCOMPtr|.
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See |nsCOMPtr::operator->|, |nsCOMPtr::operator*|, et al.
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*/
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{
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private:
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#ifndef NSCAP_NO_MEMBER_USING_DECLARATIONS
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using T::AddRef;
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using T::Release;
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#else
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nsrefcnt AddRef();
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nsrefcnt Release();
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#endif
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void operator delete( void* ); // NOT TO BE IMPLEMENTED
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// declaring |operator delete| private makes calling delete on an interface pointer a compile error
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nsDerivedSafe& operator=( const nsDerivedSafe& ); // NOT TO BE IMPLEMENTED
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// you may not call |operator=()| through a dereferenced |nsCOMPtr|, because you'd get the wrong one
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};
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#if defined(NSCAP_NO_MEMBER_USING_DECLARATIONS) && defined(NSCAP_NEED_UNUSED_VIRTUAL_IMPLEMENTATIONS)
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template <class T>
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nsrefcnt
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nsDerivedSafe<T>::AddRef()
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{
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return 0;
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}
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template <class T>
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nsrefcnt
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nsDerivedSafe<T>::Release()
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{
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return 0;
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}
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#endif
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template <class T>
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struct nsDontQueryInterface
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/*
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...
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*/
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{
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explicit
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nsDontQueryInterface( T* aRawPtr )
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: mRawPtr(aRawPtr)
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{
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// nothing else to do here
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}
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T* mRawPtr;
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};
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template <class T>
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inline
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nsDontQueryInterface<T>
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dont_QueryInterface( T* aRawPtr )
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{
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return nsDontQueryInterface<T>(aRawPtr);
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}
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struct nsQueryInterface
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{
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// explicit
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nsQueryInterface( nsISupports* aRawPtr, nsresult* error = 0 )
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: mRawPtr(aRawPtr),
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mErrorPtr(error)
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{
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// nothing else to do here
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}
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nsISupports* mRawPtr;
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nsresult* mErrorPtr;
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};
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inline
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nsQueryInterface
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do_QueryInterface( nsISupports* aRawPtr, nsresult* error = 0 )
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{
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return nsQueryInterface(aRawPtr, error);
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}
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template <class T>
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struct nsDontAddRef
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/*
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...cooperates with |nsCOMPtr| to allow you to assign in a pointer _without_
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|AddRef|ing it. You would rarely use this directly, but rather through the
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machinery of |getter_AddRefs| in the argument list to functions that |AddRef|
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their results before returning them to the caller.
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See also |getter_AddRefs()| and |class nsGetterAddRefs|.
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*/
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{
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explicit
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nsDontAddRef( T* aRawPtr )
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: mRawPtr(aRawPtr)
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{
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// nothing else to do here
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}
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T* mRawPtr;
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};
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template <class T>
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inline
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nsDontAddRef<T>
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dont_AddRef( T* aRawPtr )
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/*
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...makes typing easier, because it deduces the template type, e.g.,
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you write |dont_AddRef(fooP)| instead of |nsDontAddRef<IFoo>(fooP)|.
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Like the class it is shorthand for, you would rarely use this directly,
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but rather through |getter_AddRefs|.
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*/
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{
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return nsDontAddRef<T>(aRawPtr);
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}
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class nsCOMPtr_base
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{
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public:
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nsCOMPtr_base( nsISupports* rawPtr = 0 )
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: mRawPtr(rawPtr)
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{
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// nothing else to do here
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}
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~nsCOMPtr_base()
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{
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if ( mRawPtr )
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NSCAP_RELEASE(mRawPtr);
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}
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NS_EXPORT void assign_with_AddRef( nsISupports* );
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NS_EXPORT void assign_with_QueryInterface( nsISupports*, const nsIID&, nsresult* );
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NS_EXPORT void** begin_assignment();
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protected:
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nsISupports* mRawPtr;
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};
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template <class T>
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class nsCOMPtr : private nsCOMPtr_base
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/*
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...
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*/
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{
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public:
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typedef T element_type;
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nsCOMPtr()
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// : nsCOMPtr_base(0)
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{
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// nothing else to do here
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}
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nsCOMPtr( const nsQueryInterface& aSmartPtr )
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// : nsCOMPtr_base(0)
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{
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assign_with_QueryInterface(aSmartPtr.mRawPtr, T::IID(), aSmartPtr.mErrorPtr);
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}
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nsCOMPtr( const nsDontAddRef<T>& aSmartPtr )
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: nsCOMPtr_base(aSmartPtr.mRawPtr)
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{
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// nothing else to do here
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}
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nsCOMPtr( const nsDontQueryInterface<T>& aSmartPtr )
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: nsCOMPtr_base(aSmartPtr.mRawPtr)
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{
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if ( mRawPtr )
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NSCAP_ADDREF(mRawPtr);
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}
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nsCOMPtr( const nsCOMPtr<T>& aSmartPtr )
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: nsCOMPtr_base(aSmartPtr.mRawPtr)
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{
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if ( mRawPtr )
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NSCAP_ADDREF(mRawPtr);
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}
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nsCOMPtr<T>&
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operator=( const nsQueryInterface& rhs )
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{
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assign_with_QueryInterface(rhs.mRawPtr, T::IID(), rhs.mErrorPtr);
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return *this;
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}
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nsCOMPtr<T>&
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operator=( const nsDontAddRef<T>& rhs )
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{
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if ( mRawPtr )
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NSCAP_RELEASE(mRawPtr);
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mRawPtr = rhs.mRawPtr;
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return *this;
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}
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nsCOMPtr<T>&
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operator=( const nsDontQueryInterface<T>& rhs )
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{
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assign_with_AddRef(rhs.mRawPtr);
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return *this;
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}
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nsCOMPtr<T>&
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operator=( const nsCOMPtr& rhs )
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{
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assign_with_AddRef(rhs.mRawPtr);
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return *this;
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}
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nsDerivedSafe<T>*
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get() const
|
|
// returns a |nsDerivedSafe<T>*| to deny clients the use of |AddRef| and |Release|
|
|
{
|
|
return NSCAP_REINTERPRET_CAST(nsDerivedSafe<T>*, mRawPtr);
|
|
}
|
|
|
|
nsDerivedSafe<T>*
|
|
operator->() const
|
|
// returns a |nsDerivedSafe<T>*| to deny clients the use of |AddRef| and |Release|
|
|
{
|
|
NS_PRECONDITION(mRawPtr != 0, "You can't dereference a NULL nsCOMPtr with operator->().");
|
|
return get();
|
|
}
|
|
|
|
nsDerivedSafe<T>&
|
|
operator*() const
|
|
// returns a |nsDerivedSafe<T>*| to deny clients the use of |AddRef| and |Release|
|
|
{
|
|
NS_PRECONDITION(mRawPtr != 0, "You can't dereference a NULL nsCOMPtr with operator*().");
|
|
return *get();
|
|
}
|
|
|
|
operator nsDerivedSafe<T>*() const
|
|
{
|
|
return get();
|
|
}
|
|
|
|
#if 0
|
|
private:
|
|
friend class nsGetterAddRefs<T>;
|
|
|
|
/*
|
|
In a perfect world, the following member function, |StartAssignment|, would be private.
|
|
It is and should be only accessed by the closely related class |nsGetterAddRefs<T>|.
|
|
|
|
Unfortunately, some compilers---most notably VC++5.0---fail to grok the
|
|
friend declaration above or in any alternate acceptable form. So, physically
|
|
it will be public (until our compilers get smarter); but it is not to be
|
|
considered part of the logical public interface.
|
|
*/
|
|
#endif
|
|
|
|
T**
|
|
StartAssignment()
|
|
{
|
|
return NSCAP_REINTERPRET_CAST(T**, begin_assignment());
|
|
}
|
|
};
|
|
|
|
|
|
template <class T>
|
|
class nsGetterAddRefs
|
|
/*
|
|
...
|
|
|
|
This class is designed to be used for anonymous temporary objects in the
|
|
argument list of calls that return COM interface pointers, e.g.,
|
|
|
|
nsCOMPtr<IFoo> fooP;
|
|
...->QueryInterface(iid, nsGetterAddRefs<IFoo>(fooP))
|
|
...->QueryInterface(iid, getter_AddRefs(fooP))
|
|
|
|
When initialized with a |nsCOMPtr|, as in the example above, it returns
|
|
a |void**| (or |T**| if needed) that the outer call (|QueryInterface| in this
|
|
case) can fill in. When this temporary object goes out of scope, just after
|
|
the call returns, its destructor assigned the resulting interface pointer, i.e.,
|
|
|QueryInterface|s result, into the |nsCOMPtr| it was initialized with.
|
|
|
|
See also |nsGetterDoesntAddRef|.
|
|
*/
|
|
{
|
|
public:
|
|
explicit
|
|
nsGetterAddRefs( nsCOMPtr<T>& aSmartPtr )
|
|
: mTargetSmartPtr(aSmartPtr)
|
|
{
|
|
// nothing else to do
|
|
}
|
|
|
|
operator void**()
|
|
{
|
|
// NS_PRECONDITION(mTargetSmartPtr != 0, "getter_AddRefs into no destination");
|
|
return NSCAP_REINTERPRET_CAST(void**, mTargetSmartPtr.StartAssignment());
|
|
}
|
|
|
|
T*&
|
|
operator*()
|
|
{
|
|
// NS_PRECONDITION(mTargetSmartPtr != 0, "getter_AddRefs into no destination");
|
|
return *(mTargetSmartPtr.StartAssignment());
|
|
}
|
|
|
|
operator T**()
|
|
{
|
|
// NS_PRECONDITION(mTargetSmartPtr != 0, "getter_AddRefs into no destination");
|
|
return mTargetSmartPtr.StartAssignment();
|
|
}
|
|
|
|
private:
|
|
nsCOMPtr<T>& mTargetSmartPtr;
|
|
};
|
|
|
|
template <class T>
|
|
inline
|
|
nsGetterAddRefs<T>
|
|
getter_AddRefs( nsCOMPtr<T>& aSmartPtr )
|
|
/*
|
|
Used around a |nsCOMPtr| when
|
|
...makes the class |nsGetterAddRefs<T>| invisible.
|
|
*/
|
|
{
|
|
return nsGetterAddRefs<T>(aSmartPtr);
|
|
}
|
|
|
|
|
|
|
|
|
|
#endif // !defined(nsCOMPtr_h___)
|