LCOV - app.info - objdir/dist/include/nsTPromiseFlatString.h

LCOV - code coverage report
| Current view: | directory - objdir/dist/include - nsTPromiseFlatString.h (source / functions) |  | Found | Hit | Coverage |
| Test: | app.info | Lines: | 13 | 13 | 100.0 %
| Date: | 2012-06-02 | Functions: | 10 | 8 | 80.0 %

           1                 : /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
           2                 : /* vim:set ts=2 sw=2 sts=2 et cindent: */
           3                 : /* ***** BEGIN LICENSE BLOCK *****
           4                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
           5                 :  *
           6                 :  * The contents of this file are subject to the Mozilla Public License Version
           7                 :  * 1.1 (the "License"); you may not use this file except in compliance with
           8                 :  * the License. You may obtain a copy of the License at
           9                 :  * http://www.mozilla.org/MPL/
          10                 :  *
          11                 :  * Software distributed under the License is distributed on an "AS IS" basis,
          12                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
          13                 :  * for the specific language governing rights and limitations under the
          14                 :  * License.
          15                 :  *
          16                 :  * The Original Code is Mozilla.
          17                 :  *
          18                 :  * The Initial Developer of the Original Code is IBM Corporation.
          19                 :  * Portions created by IBM Corporation are Copyright (C) 2003
          20                 :  * IBM Corporation. All Rights Reserved.
          21                 :  *
          22                 :  * Contributor(s):
          23                 :  *   Scott Collins <scc@mozilla.org> (original author)
          24                 :  *   Darin Fisher <darin@meer.net>
          25                 :  *
          26                 :  * Alternatively, the contents of this file may be used under the terms of
          27                 :  * either the GNU General Public License Version 2 or later (the "GPL"), or
          28                 :  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
          29                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
          30                 :  * of those above. If you wish to allow use of your version of this file only
          31                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
          32                 :  * use your version of this file under the terms of the MPL, indicate your
          33                 :  * decision by deleting the provisions above and replace them with the notice
          34                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
          35                 :  * the provisions above, a recipient may use your version of this file under
          36                 :  * the terms of any one of the MPL, the GPL or the LGPL.
          37                 :  *
          38                 :  * ***** END LICENSE BLOCK ***** */
          39                 :
          40                 :
          41                 :   /**
          42                 :    * NOTE:
          43                 :    *
          44                 :    * Try to avoid flat strings.  |PromiseFlat[C]String| will help you as a last
          45                 :    * resort, and this may be necessary when dealing with legacy or OS calls,
          46                 :    * but in general, requiring a null-terminated array of characters kills many
          47                 :    * of the performance wins the string classes offer.  Write your own code to
          48                 :    * use |nsA[C]String&|s for parameters.  Write your string proccessing
          49                 :    * algorithms to exploit iterators.  If you do this, you will benefit from
          50                 :    * being able to chain operations without copying or allocating and your code
          51                 :    * will be significantly more efficient.  Remember, a function that takes an
          52                 :    * |const nsA[C]String&| can always be passed a raw character pointer by
          53                 :    * wrapping it (for free) in a |nsDependent[C]String|.  But a function that
          54                 :    * takes a character pointer always has the potential to force allocation and
          55                 :    * copying.
          56                 :    *
          57                 :    *
          58                 :    * How to use it:
          59                 :    *
          60                 :    * A |nsPromiseFlat[C]String| doesn't necessarily own the characters it
          61                 :    * promises.  You must never use it to promise characters out of a string
          62                 :    * with a shorter lifespan.  The typical use will be something like this:
          63                 :    *
          64                 :    *   SomeOSFunction( PromiseFlatCString(aCString).get() ); // GOOD
          65                 :    *
          66                 :    * Here's a BAD use:
          67                 :    *
          68                 :    *  const char* buffer = PromiseFlatCString(aCString).get();
          69                 :    *  SomeOSFunction(buffer); // BAD!! |buffer| is a dangling pointer
          70                 :    *
          71                 :    * The only way to make one is with the function |PromiseFlat[C]String|,
          72                 :    * which produce a |const| instance.  ``What if I need to keep a promise
          73                 :    * around for a little while?'' you might ask.  In that case, you can keep a
          74                 :    * reference, like so
          75                 :    *
          76                 :    *   const nsPromiseFlatString& flat = PromiseFlatString(aString);
          77                 :    *     // this reference holds the anonymous temporary alive, but remember,
          78                 :    *     // it must _still_ have a lifetime shorter than that of |aString|
          79                 :    *
          80                 :    *  SomeOSFunction(flat.get());
          81                 :    *  SomeOtherOSFunction(flat.get());
          82                 :    *
          83                 :    *
          84                 :    * How does it work?
          85                 :    *
          86                 :    * A |nsPromiseFlat[C]String| is just a wrapper for another string.  If you
          87                 :    * apply it to a string that happens to be flat, your promise is just a
          88                 :    * dependent reference to the string's data.  If you apply it to a non-flat
          89                 :    * string, then a temporary flat string is created for you, by allocating and
          90                 :    * copying.  In the event that you end up assigning the result into a sharing
          91                 :    * string (e.g., |nsTString|), the right thing happens.
          92                 :    */
          93                 :
          94                 : class nsTPromiseFlatString_CharT : public nsTString_CharT
          95         2039739 :   {
          96                 :     public:
          97                 :
          98                 :       typedef nsTPromiseFlatString_CharT    self_type;
          99                 :
         100                 :     private:
         101                 :
         102                 :       void Init( const substring_type& );
         103                 :
         104                 :         // NOT TO BE IMPLEMENTED
         105                 :       void operator=( const self_type& );
         106                 :
         107                 :         // NOT TO BE IMPLEMENTED
         108                 :       nsTPromiseFlatString_CharT();
         109                 :
         110                 :     public:
         111                 :
         112                 :       explicit
         113         2024189 :       nsTPromiseFlatString_CharT( const substring_type& str )
         114         2024189 :         : string_type()
         115                 :         {
         116         2024189 :           Init(str);
         117         2024189 :         }
         118                 :
         119                 :       explicit
         120           15550 :       nsTPromiseFlatString_CharT( const substring_tuple_type& tuple )
         121           15550 :         : string_type()
         122                 :         {
         123                 :           // nothing else to do here except assign the value of the tuple
         124                 :           // into ourselves.
         125           15550 :           Assign(tuple);
         126           15550 :         }
         127                 :   };
         128                 :
         129                 :   // e.g., PromiseFlatCString(Substring(s))
         130                 : inline
         131                 : const nsTPromiseFlatString_CharT
         132         2021579 : TPromiseFlatString_CharT( const nsTSubstring_CharT& frag )
         133                 :   {
         134         2021579 :     return nsTPromiseFlatString_CharT(frag);
         135                 :   }
         136                 :
         137                 :   // e.g., PromiseFlatCString(a + b)
         138                 : inline
         139                 : const nsTPromiseFlatString_CharT
         140           15550 : TPromiseFlatString_CharT( const nsTSubstringTuple_CharT& tuple )
         141                 :   {
         142           15550 :     return nsTPromiseFlatString_CharT(tuple);
         143                 :   }

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