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