1 files changed, 49 insertions, 0 deletions
diff --git a/xpcom/glue/nsIInterfaceRequestorUtils.h b/xpcom/glue/nsIInterfaceRequestorUtils.h
new file mode 100644
index 0000000000..718cf387b5
--- /dev/null
+++ b/xpcom/glue/nsIInterfaceRequestorUtils.h
@@ -0,0 +1,49 @@
+/* -*- 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 __nsInterfaceRequestorUtils_h
+#define __nsInterfaceRequestorUtils_h
+
+#include "nsCOMPtr.h"
+
+// a type-safe shortcut for calling the |GetInterface()| member function
+// T must inherit from nsIInterfaceRequestor, but the cast may be ambiguous.
+template<class T, class DestinationType>
+inline nsresult
+CallGetInterface(T* aSource, DestinationType** aDestination)
+{
+  NS_PRECONDITION(aSource, "null parameter");
+  NS_PRECONDITION(aDestination, "null parameter");
+
+  return aSource->GetInterface(NS_GET_TEMPLATE_IID(DestinationType),
+                               reinterpret_cast<void**>(aDestination));
+}
+
+class MOZ_STACK_CLASS nsGetInterface final : public nsCOMPtr_helper
+{
+public:
+  nsGetInterface(nsISupports* aSource, nsresult* aError)
+    : mSource(aSource)
+    , mErrorPtr(aError)
+  {
+  }
+
+  virtual nsresult NS_FASTCALL operator()(const nsIID&, void**) const
+    override;
+
+private:
+  nsISupports* MOZ_NON_OWNING_REF mSource;
+  nsresult* mErrorPtr;
+};
+
+inline const nsGetInterface
+do_GetInterface(nsISupports* aSource, nsresult* aError = 0)
+{
+  return nsGetInterface(aSource, aError);
+}
+
+#endif // __nsInterfaceRequestorUtils_h
+