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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: */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

   /**

    * NOTE:

    *

    * Try to avoid flat strings.  |PromiseFlat[C]String| will help you as a last

    * resort, and this may be necessary when dealing with legacy or OS calls,

    * but in general, requiring a null-terminated array of characters kills many

    * of the performance wins the string classes offer.  Write your own code to

    * use |nsA[C]String&|s for parameters.  Write your string proccessing

    * algorithms to exploit iterators.  If you do this, you will benefit from

    * being able to chain operations without copying or allocating and your code

    * will be significantly more efficient.  Remember, a function that takes an

    * |const nsA[C]String&| can always be passed a raw character pointer by

    * wrapping it (for free) in a |nsDependent[C]String|.  But a function that

    * takes a character pointer always has the potential to force allocation and

    * copying.

    *

    *

    * How to use it:

    *

    * A |nsPromiseFlat[C]String| doesn't necessarily own the characters it

    * promises.  You must never use it to promise characters out of a string

    * with a shorter lifespan.  The typical use will be something like this:

    *

    *   SomeOSFunction( PromiseFlatCString(aCSubstring).get() ); // GOOD

    *

    * Here's a BAD use:

    *

    *  const char* buffer = PromiseFlatCString(aCSubstring).get();

    *  SomeOSFunction(buffer); // BAD!! |buffer| is a dangling pointer

    *

    * The only way to make one is with the function |PromiseFlat[C]String|,

    * which produce a |const| instance.  ``What if I need to keep a promise

    * around for a little while?'' you might ask.  In that case, you can keep a

    * reference, like so

    *

    *   const nsCString& flat = PromiseFlatString(aCSubstring);

    *     // this reference holds the anonymous temporary alive, but remember,

    *     // it must _still_ have a lifetime shorter than that of |aCSubstring|

    *

    *  SomeOSFunction(flat.get());

    *  SomeOtherOSFunction(flat.get());

    *

    *

    * How does it work?

    *

    * A |nsPromiseFlat[C]String| is just a wrapper for another string.  If you

    * apply it to a string that happens to be flat, your promise is just a

    * dependent reference to the string's data.  If you apply it to a non-flat

    * string, then a temporary flat string is created for you, by allocating and

    * copying.  In the event that you end up assigning the result into a sharing

    * string (e.g., |nsTString|), the right thing happens.

    */

 class nsTPromiseFlatString_CharT : public nsTString_CharT

   {

     public:

       typedef nsTPromiseFlatString_CharT    self_type;

     private:

       void Init( const substring_type& );

         // NOT TO BE IMPLEMENTED

       void operator=( const self_type& ) MOZ_DELETE;

         // NOT TO BE IMPLEMENTED

       nsTPromiseFlatString_CharT() MOZ_DELETE;

         // NOT TO BE IMPLEMENTED

       nsTPromiseFlatString_CharT( const string_type& str ) MOZ_DELETE;

     public:

       explicit

       nsTPromiseFlatString_CharT( const substring_type& str )

         : string_type()

         {

           Init(str);

         }

       explicit

       nsTPromiseFlatString_CharT( const substring_tuple_type& tuple )

         : string_type()

         {

           // nothing else to do here except assign the value of the tuple

           // into ourselves.

           Assign(tuple);

         }

   };

 // We template this so that the constructor is chosen based on the type of the

 // parameter. This allows us to reject attempts to promise a flat flat string.

 template<class T>

 const nsTPromiseFlatString_CharT

 TPromiseFlatString_CharT( const T& string )

   {

     return nsTPromiseFlatString_CharT(string);

   }