gecko-dev/xpcom/glue/nsIInterfaceRequestorUtils.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 __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 NS_COM_GLUE nsGetInterface : public nsCOMPtr_helper
{
public:
  nsGetInterface(nsISupports* aSource, nsresult* aError)
    : mSource(aSource)
    , mErrorPtr(aError)
  {
  }

  virtual nsresult NS_FASTCALL operator()(const nsIID&, void**) const;

private:
  nsISupports* mSource;
  nsresult* mErrorPtr;
};

inline const nsGetInterface
do_GetInterface(nsISupports* aSource, nsresult* aError = 0)
{
  return nsGetInterface(aSource, aError);
}

#endif // __nsInterfaceRequestorUtils_h