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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