gecko-dev/xpcom/glue/nsIWeakReferenceUtils.h

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 *   Scott Collins <scc@mozilla.org> (Original Author)
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#ifndef nsIWeakReferenceUtils_h__
#define nsIWeakReferenceUtils_h__

#ifndef nsCOMPtr_h__
#include "nsCOMPtr.h"
#endif

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 )
  {
    NS_PRECONDITION(aSource, "null parameter");
    NS_PRECONDITION(aDestination, "null parameter");

    return aSource->QueryReferent(NS_GET_IID(DestinationType),
                                  NS_REINTERPRET_CAST(void**, aDestination));
  }


class NS_COM nsQueryReferent : public nsCOMPtr_helper
  {
    public:
      nsQueryReferent( nsIWeakReference* aWeakPtr, nsresult* error )
          : mWeakPtr(aWeakPtr),
            mErrorPtr(error)
        {
          // nothing else to do here
        }

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

    private:
      nsIWeakReference*  mWeakPtr;
      nsresult*          mErrorPtr;
  };

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



class NS_COM nsGetWeakReference : public nsCOMPtr_helper
  {
    public:
      nsGetWeakReference( nsISupports* aRawPtr, nsresult* error )
          : mRawPtr(aRawPtr),
            mErrorPtr(error)
        {
          // nothing else to do here
        }

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

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

  /**
   * |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
const nsGetWeakReference
do_GetWeakReference( nsISupports* aRawPtr, nsresult* error = 0 )
  {
    return nsGetWeakReference(aRawPtr, error);
  }

inline
void
do_GetWeakReference( nsIWeakReference* aRawPtr, nsresult* error = 0 )
  {
    // This signature exists soley 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 soley 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 soley 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>.
  }



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

#endif