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// Author:  29/05/2013
// Following proposal by Markus Frank

 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *

#include "TGeoExtension.h"


//   TGeoExtension - ABC for user objects attached to TGeoVolume or TGeoNode.
//                   Provides interface for getting a reference (grab) and
//                   releasing the extension object (release), allowing for 
//                   derived classes to implement reference counted sharing.
//                   The user who should attach extensions to logical volumes
//                   or nodes BEFORE applying misalignment information so that 
//                   these will be available to all copies.


//   TGeoRCExtension - Reference counted extension which has a pointer to and 
//                   owns a user defined TObject. This class can be used as 
//                   model for a reference counted derivation from TGeoExtension.

// Note: Creating a TGeoRCExtension with new() automatically grabs it, but the 
// creator has to Release it before the pointer gets out of scope. 
// The following sequence is valid:
//   // producer:
//   TGeoRCExtension *ext = new TGeoRCExtension();
//   some_TGeoVolume->SetUserExtension(ext);
//   ext->Release();
//   // user:
//   TGeoRCExtension *ext = dynamic_cast<TGeoRCExtension*>(some_TGeoVolume->GrabUserExtension());
//   // ... use extension
//   ext->Release();
// The extension is going to be released by the TGeoVolume holder at the destruction
// or when calling SetUserExtension(0).
// The following usage is not correct:
//   some_TGeoVolume->SetUserExtension(new TGeoRCExtension())
// since the producer code does not release the extension.
// One cannot call directly "delete ext" nor allocate an extension on the stack,
// since the destructor is protected. Use Release instead.