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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla.
*
* The Initial Developer of the Original Code is IBM Corporation.
* Portions created by IBM Corporation are Copyright (C) 2003
* IBM Corporation. All Rights Reserved.
*
* Contributor(s):
* Darin Fisher <darin@meer.net>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef nsObsoleteAString_h___
#define nsObsoleteAString_h___
/*
STRING INTERNALS
This file defines nsObsoleteAString and nsObsoleteACString. These are
abstract classes (interfaces), containing only virtual functions
corresponding to the FROZEN nsA[C]String classes. They exist to provide
the new non-abstract nsA[C]String classes with a mechanism to maintain
backwards binary compatability.
From a binary point-of-view, the new nsA[C]String classes appear to have a
vtable pointer to the vtable of nsObsoleteA[C]StringThunk.
nsObsoleteA[C]StringThunk is a subclass of nsObsoleteA[C]String that serves
as a simple bridge between the virtual functions that make up the FROZEN
nsA[C]String contract and the new ns[C]Substring, which is now our only
subclass of nsA[C]String.
The methods on the new nsA[C]String are now all non-virtual. This reduces
codesize at the callsite, and reduces the number of memory dereferences and
jumps required to invoke a method on nsA[C]String. The result is improved
performance and reduced codesize. However, to maintain binary
compatibility, each method on nsA[C]String must check the value of its
vtable to determine if it corresponds to the built-in implementation of
nsObsoleteA[C]String (i.e., the address of the canonical vtable). If it
does, then the vtable can be ignored, and the nsA[C]String object (i.e.,
|this|) can be cast to ns[C]Substring directly. In which case, the
nsA[C]String methods can be satisfied by invoking the corresponding methods
directly on ns[C]Substring. If the vtable address does not correspond to
the built-in implementation, then the virtual functions on
nsObsoleteA[C]String must be invoked instead.
So, if a nsA[C]String reference corresponds to an external implementation
(such as the old nsEmbed[C]String that shipped with previous versions of
Mozilla), then methods invoked on that nsA[C]String will still act like
virtual function calls. This ensures binary compatibility while avoiding
virtual function calls in most cases.
Finally, nsObsoleteA[C]String (i.e., the FROZEN nsA[C]String vtable) is
now a DEPRECATED interface. See nsStringAPI.h and nsEmbedString.h for
the new preferred way to access nsA[C]String references in an external
component or Gecko embedding application.
*/
#ifndef nsStringFwd_h___
#include "nsStringFwd.h"
#endif
#ifndef nscore_h___
#include "nscore.h"
#endif
// declare nsObsoleteAString
#include "string-template-def-unichar.h"
#include "nsTObsoleteAString.h"
#include "string-template-undef.h"
// declare nsObsoleteACString
#include "string-template-def-char.h"
#include "nsTObsoleteAString.h"
#include "string-template-undef.h"
#endif // !defined(nsObsoleteAString_h___)
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