The GtkRadiant sources as originally released under the GPL license.

libs/generic/static.h

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+/*
+Copyright (C) 2001-2006, William Joseph.
+All Rights Reserved.
+
+This file is part of GtkRadiant.
+
+GtkRadiant is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+GtkRadiant is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GtkRadiant; if not, write to the Free Software
+Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#if !defined(INCLUDED_GENERIC_STATIC_H)
+#define INCLUDED_GENERIC_STATIC_H
+
+/// \file
+/// \brief Template techniques for instantiating singletons.
+
+#include <cstddef>
+
+/// \brief A singleton which is statically initialised.
+///
+/// \param Type The singleton object type.
+///
+/// \dontinclude generic/static.cpp
+/// \skipline Static example
+/// \until end example
+template<typename Type>
+class Static
+{
+  static Type m_instance;
+public:
+  static Type& instance()
+  {
+    return m_instance;
+  }
+};
+
+template<typename Type>
+Type Static<Type>::m_instance;
+
+
+/// \brief A singleton which is lazily initialised.
+/// The instance is constructed the first time it is referenced, and is never destroyed.
+///
+/// \param Type The singleton object type.
+///
+/// \dontinclude generic/static.cpp
+/// \skipline LazyStatic example
+/// \until end example
+template<typename Type>
+class LazyStatic
+{
+  static Type* m_instance; // this will be initialised to 0 by the CRT, according to the c++ standard
+public:
+  static Type& instance()
+  {
+    if(m_instance == 0)
+    {
+      m_instance = new Type; // allocate using 'new' to get the correct alignment
+    }
+    return *m_instance;
+  }
+};
+
+template<typename Type>
+Type* LazyStatic<Type>::m_instance;
+
+
+/// \brief A singleton which keeps a count of the number of times it is referenced.
+///
+/// The instance is constructed when its reference count changes from 0 to 1 and destroyed when its reference count changes from 1 to 0.
+/// Use with SmartStatic.
+///
+/// \param Type The singleton object type.
+template<typename Type>
+class CountedStatic
+{
+  static std::size_t m_refcount; // this will be initialised to 0 by the CRT, according to the c++ standard
+  static Type* m_instance;
+public:
+  static Type& instance()
+  {
+    return *m_instance;
+  }
+  static void capture()
+  {
+    if(++m_refcount == 1)
+    {
+      m_instance = new Type; // allocate using 'new' to get the correct alignment
+    }
+  }
+  static void release()
+  {
+    if(--m_refcount == 0)
+    {
+      delete m_instance;
+    }
+  }
+};
+
+template<typename Type>
+std::size_t CountedStatic<Type>::m_refcount; // this will be initialised to 0 by the CRT, according to the c++ standard
+template<typename Type>
+Type* CountedStatic<Type>::m_instance;
+
+/// \brief A reference to a CountedStatic.
+/// Guarantees that CountedStatic<Type> will be constructed for the lifetime of this object.
+///
+/// \param Type The type parameter of the CountedStatic to reference.
+///
+/// \dontinclude generic/static.cpp
+/// \skipline SmartStatic example
+/// \until end example
+template<typename Type>
+class SmartStatic
+{
+public:
+  SmartStatic()
+  {
+    CountedStatic<Type>::capture();
+  }
+  ~SmartStatic()
+  {
+    CountedStatic<Type>::release();
+  }
+  Type& instance()
+  {
+    return CountedStatic<Type>::instance();
+  }
+};
+
+
+#endif