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public/branchingsingleton.h

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+//========= Copyright <20> 1996-2005, Valve Corporation, All rights reserved. ============//
+//
+// Purpose: Macros for defining branching singletons.
+//
+//			A branching singleton defines a singleton class within another class, and subclasses
+//			of the outer class can automatically expand on that singleton at their node in the
+//			class branching tree with the confidence that changes will be reflected in all
+//			subclasses.
+//
+//			The primary reason to have a branching singleton is to centralize management code
+//			without being tied explicitly to one interface. The interface can possibly change
+//			vastly as it gets passed down the tree to the point where all the original functions
+//			are stubs and the interface uses an entirely different set of functions.
+//
+// $NoKeywords: $
+//=============================================================================//
+
+#ifndef BRANCHINGSINGLETON_H
+#define BRANCHINGSINGLETON_H
+#ifdef _WIN32
+#pragma once
+#endif
+
+
+#define START_BRANCHING_SINGLETON_DEFINITION_NOBASE( classname ) class classname
+
+#define START_BRANCHING_SINGLETON_DEFINITION( classname ) class classname : public Base##classname
+
+#define _END_BRANCHING_SINGLETON_DEFINITION( classname );\
+	static classname *Get_##classname##_Static( void )\
+	{\
+		static classname s_Singleton;\
+		return &s_Singleton;\
+	}\
+	\
+	virtual Root##classname *Get_##classname##( void )\
+	{\
+		return Get_##classname##_Static();\
+	}\
+	typedef classname Base##classname;
+
+#define END_BRANCHING_SINGLETON_DEFINITION( classname ) _END_BRANCHING_SINGLETON_DEFINITION( classname )
+
+#define END_BRANCHING_SINGLETON_DEFINITION_NOBASE( classname );\
+	typedef classname Root##classname;\
+	_END_BRANCHING_SINGLETON_DEFINITION( classname );
+
+#endif //#ifndef BRANCHINGSINGLETON_H