xpcom/glue/nsIWeakReferenceUtils.h

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  15  * The Original Code is mozilla.org code.
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  22  * Contributor(s):
  23  *   Scott Collins <scc@mozilla.org> (Original Author)
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  38
  39 #ifndef nsIWeakReferenceUtils_h__
  40 #define nsIWeakReferenceUtils_h__
  41
  42 #ifndef nsCOMPtr_h__
  43 #include "nsCOMPtr.h"
  44 #endif
  45
  46 typedef nsCOMPtr<nsIWeakReference> nsWeakPtr;
  47
  48 /**
  49  *
  50  */
  51
  52 // a type-safe shortcut for calling the |QueryReferent()| member function
  53 // T must inherit from nsIWeakReference, but the cast may be ambiguous.
  54 template <class T, class DestinationType>
  55 inline
  56 nsresult
  57 CallQueryReferent( T* aSource, DestinationType** aDestination )
  58   {
  59     NS_PRECONDITION(aSource, "null parameter");
  60     NS_PRECONDITION(aDestination, "null parameter");
  61
  62     return aSource->QueryReferent(NS_GET_TEMPLATE_IID(DestinationType),
  63                                   reinterpret_cast<void**>(aDestination));
  64   }
  65
  66
  67 class NS_COM_GLUE nsQueryReferent : public nsCOMPtr_helper
  68   {
  69     public:
  70       nsQueryReferent( nsIWeakReference* aWeakPtr, nsresult* error )
  71           : mWeakPtr(aWeakPtr),
  72             mErrorPtr(error)
  73         {
  74           // nothing else to do here
  75         }
  76
  77       virtual nsresult NS_FASTCALL operator()( const nsIID& aIID, void** ) const;
  78
  79     private:
  80       nsIWeakReference*  mWeakPtr;
  81       nsresult*          mErrorPtr;
  82   };
  83
  84 inline
  85 const nsQueryReferent
  86 do_QueryReferent( nsIWeakReference* aRawPtr, nsresult* error = 0 )
  87   {
  88     return nsQueryReferent(aRawPtr, error);
  89   }
  90
  91
  92   /**
  93    * Deprecated, use |do_GetWeakReference| instead.
  94    */
  95 extern NS_COM_GLUE
  96 nsIWeakReference*
  97 NS_GetWeakReference( nsISupports* , nsresult* aResult=0 );
  98
  99   /**
 100    * |do_GetWeakReference| is a convenience function that bundles up all the work needed
 101    * to get a weak reference to an arbitrary object, i.e., the |QueryInterface|, test, and
 102    * call through to |GetWeakReference|, and put it into your |nsCOMPtr|.
 103    * It is specifically designed to cooperate with |nsCOMPtr| (or |nsWeakPtr|) like so:
 104    * |nsWeakPtr myWeakPtr = do_GetWeakReference(aPtr);|.
 105    */
 106 inline
 107 already_AddRefed<nsIWeakReference>
 108 do_GetWeakReference( nsISupports* aRawPtr, nsresult* error = 0 )
 109   {
 110     return NS_GetWeakReference(aRawPtr, error);
 111   }
 112
 113 inline
 114 void
 115 do_GetWeakReference( nsIWeakReference* aRawPtr, nsresult* error = 0 )
 116   {
 117     // This signature exists solely to _stop_ you from doing a bad thing.
 118     //  Saying |do_GetWeakReference()| on a weak reference itself,
 119     //  is very likely to be a programmer error.
 120   }
 121
 122 template <class T>
 123 inline
 124 void
 125 do_GetWeakReference( already_AddRefed<T>& )
 126   {
 127     // This signature exists solely to _stop_ you from doing the bad thing.
 128     //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
 129     //  someone else is an automatic leak.  See <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
 130   }
 131
 132 template <class T>
 133 inline
 134 void
 135 do_GetWeakReference( already_AddRefed<T>&, nsresult* )
 136   {
 137     // This signature exists solely to _stop_ you from doing the bad thing.
 138     //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
 139     //  someone else is an automatic leak.  See <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
 140   }
 141
 142 #endif