michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim:set ts=2 sw=2 sts=2 et cindent: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: 
michael@0:   /**
michael@0:    * NOTE:
michael@0:    *
michael@0:    * Try to avoid flat strings.  |PromiseFlat[C]String| will help you as a last
michael@0:    * resort, and this may be necessary when dealing with legacy or OS calls,
michael@0:    * but in general, requiring a null-terminated array of characters kills many
michael@0:    * of the performance wins the string classes offer.  Write your own code to
michael@0:    * use |nsA[C]String&|s for parameters.  Write your string proccessing
michael@0:    * algorithms to exploit iterators.  If you do this, you will benefit from
michael@0:    * being able to chain operations without copying or allocating and your code
michael@0:    * will be significantly more efficient.  Remember, a function that takes an
michael@0:    * |const nsA[C]String&| can always be passed a raw character pointer by
michael@0:    * wrapping it (for free) in a |nsDependent[C]String|.  But a function that
michael@0:    * takes a character pointer always has the potential to force allocation and
michael@0:    * copying.
michael@0:    *
michael@0:    *
michael@0:    * How to use it:
michael@0:    *
michael@0:    * A |nsPromiseFlat[C]String| doesn't necessarily own the characters it
michael@0:    * promises.  You must never use it to promise characters out of a string
michael@0:    * with a shorter lifespan.  The typical use will be something like this:
michael@0:    *
michael@0:    *   SomeOSFunction( PromiseFlatCString(aCSubstring).get() ); // GOOD
michael@0:    *
michael@0:    * Here's a BAD use:
michael@0:    *
michael@0:    *  const char* buffer = PromiseFlatCString(aCSubstring).get();
michael@0:    *  SomeOSFunction(buffer); // BAD!! |buffer| is a dangling pointer
michael@0:    *
michael@0:    * The only way to make one is with the function |PromiseFlat[C]String|,
michael@0:    * which produce a |const| instance.  ``What if I need to keep a promise
michael@0:    * around for a little while?'' you might ask.  In that case, you can keep a
michael@0:    * reference, like so
michael@0:    *
michael@0:    *   const nsCString& flat = PromiseFlatString(aCSubstring);
michael@0:    *     // this reference holds the anonymous temporary alive, but remember,
michael@0:    *     // it must _still_ have a lifetime shorter than that of |aCSubstring|
michael@0:    *
michael@0:    *  SomeOSFunction(flat.get());
michael@0:    *  SomeOtherOSFunction(flat.get());
michael@0:    *
michael@0:    *
michael@0:    * How does it work?
michael@0:    *
michael@0:    * A |nsPromiseFlat[C]String| is just a wrapper for another string.  If you
michael@0:    * apply it to a string that happens to be flat, your promise is just a
michael@0:    * dependent reference to the string's data.  If you apply it to a non-flat
michael@0:    * string, then a temporary flat string is created for you, by allocating and
michael@0:    * copying.  In the event that you end up assigning the result into a sharing
michael@0:    * string (e.g., |nsTString|), the right thing happens.
michael@0:    */
michael@0: 
michael@0: class nsTPromiseFlatString_CharT : public nsTString_CharT
michael@0:   {
michael@0:     public:
michael@0: 
michael@0:       typedef nsTPromiseFlatString_CharT    self_type;
michael@0: 
michael@0:     private:
michael@0: 
michael@0:       void Init( const substring_type& );
michael@0: 
michael@0:         // NOT TO BE IMPLEMENTED
michael@0:       void operator=( const self_type& ) MOZ_DELETE;
michael@0: 
michael@0:         // NOT TO BE IMPLEMENTED
michael@0:       nsTPromiseFlatString_CharT() MOZ_DELETE;
michael@0: 
michael@0:         // NOT TO BE IMPLEMENTED
michael@0:       nsTPromiseFlatString_CharT( const string_type& str ) MOZ_DELETE;
michael@0: 
michael@0:     public:
michael@0: 
michael@0:       explicit
michael@0:       nsTPromiseFlatString_CharT( const substring_type& str )
michael@0:         : string_type()
michael@0:         {
michael@0:           Init(str);
michael@0:         }
michael@0: 
michael@0:       explicit
michael@0:       nsTPromiseFlatString_CharT( const substring_tuple_type& tuple )
michael@0:         : string_type()
michael@0:         {
michael@0:           // nothing else to do here except assign the value of the tuple
michael@0:           // into ourselves.
michael@0:           Assign(tuple);
michael@0:         }
michael@0:   };
michael@0: 
michael@0: // We template this so that the constructor is chosen based on the type of the
michael@0: // parameter. This allows us to reject attempts to promise a flat flat string.
michael@0: template<class T>
michael@0: const nsTPromiseFlatString_CharT
michael@0: TPromiseFlatString_CharT( const T& string )
michael@0:   {
michael@0:     return nsTPromiseFlatString_CharT(string);
michael@0:   }