xpcom/glue/nsIWeakReferenceUtils.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsIWeakReferenceUtils_h__
   8 #define nsIWeakReferenceUtils_h__
   9
  10 #include "nsCOMPtr.h"
  11 #include "nsIWeakReference.h"
  12
  13 typedef nsCOMPtr<nsIWeakReference> nsWeakPtr;
  14
  15 /**
  16  *
  17  */
  18
  19 // a type-safe shortcut for calling the |QueryReferent()| member function
  20 // T must inherit from nsIWeakReference, but the cast may be ambiguous.
  21 template<class T, class DestinationType>
  22 inline nsresult
  23 CallQueryReferent(T* aSource, DestinationType** aDestination)
  24 {
  25   NS_PRECONDITION(aSource, "null parameter");
  26   NS_PRECONDITION(aDestination, "null parameter");
  27
  28   return aSource->QueryReferent(NS_GET_TEMPLATE_IID(DestinationType),
  29                                 reinterpret_cast<void**>(aDestination));
  30 }
  31
  32
  33 class nsQueryReferent : public nsCOMPtr_helper
  34 {
  35 public:
  36   nsQueryReferent(nsIWeakReference* aWeakPtr, nsresult* aError)
  37     : mWeakPtr(aWeakPtr)
  38     , mErrorPtr(aError)
  39   {
  40   }
  41
  42   virtual nsresult NS_FASTCALL operator()(const nsIID& aIID, void**) const;
  43
  44 private:
  45   nsIWeakReference*  mWeakPtr;
  46   nsresult*          mErrorPtr;
  47 };
  48
  49 inline const nsQueryReferent
  50 do_QueryReferent(nsIWeakReference* aRawPtr, nsresult* aError = 0)
  51 {
  52   return nsQueryReferent(aRawPtr, aError);
  53 }
  54
  55
  56 /**
  57  * Deprecated, use |do_GetWeakReference| instead.
  58  */
  59 extern nsIWeakReference* NS_GetWeakReference(nsISupports*,
  60                                              nsresult* aResult = 0);
  61
  62 /**
  63  * |do_GetWeakReference| is a convenience function that bundles up all the work needed
  64  * to get a weak reference to an arbitrary object, i.e., the |QueryInterface|, test, and
  65  * call through to |GetWeakReference|, and put it into your |nsCOMPtr|.
  66  * It is specifically designed to cooperate with |nsCOMPtr| (or |nsWeakPtr|) like so:
  67  * |nsWeakPtr myWeakPtr = do_GetWeakReference(aPtr);|.
  68  */
  69 inline already_AddRefed<nsIWeakReference>
  70 do_GetWeakReference(nsISupports* aRawPtr, nsresult* aError = 0)
  71 {
  72   return dont_AddRef(NS_GetWeakReference(aRawPtr, aError));
  73 }
  74
  75 inline void
  76 do_GetWeakReference(nsIWeakReference* aRawPtr, nsresult* aError = 0)
  77 {
  78   // This signature exists solely to _stop_ you from doing a bad thing.
  79   //  Saying |do_GetWeakReference()| on a weak reference itself,
  80   //  is very likely to be a programmer error.
  81 }
  82
  83 template<class T>
  84 inline void
  85 do_GetWeakReference(already_AddRefed<T>&)
  86 {
  87   // This signature exists solely to _stop_ you from doing the bad thing.
  88   //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
  89   //  someone else is an automatic leak.  See <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
  90 }
  91
  92 template<class T>
  93 inline void
  94 do_GetWeakReference(already_AddRefed<T>&, nsresult*)
  95 {
  96   // This signature exists solely to _stop_ you from doing the bad thing.
  97   //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
  98   //  someone else is an automatic leak.  See <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
  99 }
 100
 101 #endif