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112 lines
2.6 KiB
C++
112 lines
2.6 KiB
C++
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#if !defined( INCLUDED_GENERIC_STATIC_H )
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#define INCLUDED_GENERIC_STATIC_H
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/// \file
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/// \brief Template techniques for instantiating singletons.
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#include <cstddef>
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/// \brief A singleton which is statically initialised.
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///
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/// \param Type The singleton object type.
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///
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/// \dontinclude generic/static.cpp
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/// \skipline Static example
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/// \until end example
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template<typename Type>
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class Static
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{
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static Type m_instance;
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public:
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static Type& instance(){
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return m_instance;
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}
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};
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template<typename Type>
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Type Static<Type>::m_instance;
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/// \brief A singleton which is lazily initialised.
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/// The instance is constructed the first time it is referenced, and is never destroyed.
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///
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/// \param Type The singleton object type.
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///
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/// \dontinclude generic/static.cpp
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/// \skipline LazyStatic example
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/// \until end example
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template<typename Type>
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class LazyStatic
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{
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static Type* m_instance; // this will be initialised to 0 by the CRT, according to the c++ standard
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public:
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static Type& instance(){
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if ( m_instance == 0 ) {
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m_instance = new Type; // allocate using 'new' to get the correct alignment
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}
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return *m_instance;
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}
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};
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template<typename Type>
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Type * LazyStatic<Type>::m_instance;
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/// \brief A singleton which keeps a count of the number of times it is referenced.
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///
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/// The instance is constructed when its reference count changes from 0 to 1 and destroyed when its reference count changes from 1 to 0.
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/// Use with SmartStatic.
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///
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/// \param Type The singleton object type.
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template<typename Type>
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class CountedStatic
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{
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static std::size_t m_refcount; // this will be initialised to 0 by the CRT, according to the c++ standard
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static Type* m_instance;
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public:
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static Type& instance(){
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return *m_instance;
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}
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static void capture(){
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if ( ++m_refcount == 1 ) {
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m_instance = new Type; // allocate using 'new' to get the correct alignment
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}
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}
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static void release(){
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if ( --m_refcount == 0 ) {
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delete m_instance;
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}
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}
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};
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template<typename Type>
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std::size_t CountedStatic<Type>::m_refcount; // this will be initialised to 0 by the CRT, according to the c++ standard
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template<typename Type>
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Type * CountedStatic<Type>::m_instance;
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/// \brief A reference to a CountedStatic.
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/// Guarantees that CountedStatic<Type> will be constructed for the lifetime of this object.
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///
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/// \param Type The type parameter of the CountedStatic to reference.
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///
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/// \dontinclude generic/static.cpp
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/// \skipline SmartStatic example
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/// \until end example
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template<typename Type>
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class SmartStatic
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{
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public:
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SmartStatic(){
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CountedStatic<Type>::capture();
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}
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~SmartStatic(){
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CountedStatic<Type>::release();
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}
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Type& instance(){
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return CountedStatic<Type>::instance();
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}
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};
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#endif
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