gecko-dev/xpcom/base/nsIWeakReferenceUtils.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/. */

#ifndef nsIWeakReferenceUtils_h__
#define nsIWeakReferenceUtils_h__

#include "nsCOMPtr.h"
#include "nsIWeakReference.h"

typedef nsCOMPtr<nsIWeakReference> nsWeakPtr;

/**
 *
 */

// a type-safe shortcut for calling the |QueryReferent()| member function
// T must inherit from nsIWeakReference, but the cast may be ambiguous.
template <class T, class DestinationType>
inline nsresult CallQueryReferent(T* aSource, DestinationType** aDestination) {
  MOZ_ASSERT(aSource, "null parameter");
  MOZ_ASSERT(aDestination, "null parameter");

  return aSource->QueryReferent(NS_GET_TEMPLATE_IID(DestinationType),
                                reinterpret_cast<void**>(aDestination));
}

inline const nsQueryReferent do_QueryReferent(nsIWeakReference* aRawPtr,
                                              nsresult* aError = 0) {
  return nsQueryReferent(aRawPtr, aError);
}

/**
 * Deprecated, use |do_GetWeakReference| instead.
 */
extern nsIWeakReference* NS_GetWeakReference(nsISupports*,
                                             nsresult* aResult = 0);
extern nsIWeakReference* NS_GetWeakReference(nsISupportsWeakReference*,
                                             nsresult* aResult = 0);

/**
 * |do_GetWeakReference| is a convenience function that bundles up all the work
 * needed to get a weak reference to an arbitrary object, i.e., the
 * |QueryInterface|, test, and call through to |GetWeakReference|, and put it
 * into your |nsCOMPtr|. It is specifically designed to cooperate with
 * |nsCOMPtr| (or |nsWeakPtr|) like so: |nsWeakPtr myWeakPtr =
 * do_GetWeakReference(aPtr);|.
 */
inline already_AddRefed<nsIWeakReference> do_GetWeakReference(
    nsISupports* aRawPtr, nsresult* aError = 0) {
  return dont_AddRef(NS_GetWeakReference(aRawPtr, aError));
}

inline already_AddRefed<nsIWeakReference> do_GetWeakReference(
    nsISupportsWeakReference* aRawPtr, nsresult* aError = 0) {
  return dont_AddRef(NS_GetWeakReference(aRawPtr, aError));
}

inline void do_GetWeakReference(nsIWeakReference* aRawPtr,
                                nsresult* aError = 0) {
  // This signature exists solely to _stop_ you from doing a bad thing.
  //  Saying |do_GetWeakReference()| on a weak reference itself,
  //  is very likely to be a programmer error.
}

template <class T>
inline void do_GetWeakReference(already_AddRefed<T>&) {
  // This signature exists solely to _stop_ you from doing the bad thing.
  //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
  //  someone else is an automatic leak.  See
  //  <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
}

template <class T>
inline void do_GetWeakReference(already_AddRefed<T>&, nsresult*) {
  // This signature exists solely to _stop_ you from doing the bad thing.
  //  Saying |do_GetWeakReference()| on a pointer that is not otherwise owned by
  //  someone else is an automatic leak.  See
  //  <http://bugzilla.mozilla.org/show_bug.cgi?id=8221>.
}

#endif