singleton.hpp

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#ifndef LIBJMMCG_CORE_SINGLETON_HPP
#define LIBJMMCG_CORE_SINGLETON_HPP
/******************************************************************************
** Copyright © 2012 by J.M.McGuiness, coder@hussar.me.uk
**
** This library is free software; you can redistribute it and/or
** modify it under the terms of the GNU Lesser General Public
** License as published by the Free Software Foundation; either
** version 2.1 of the License, or (at your option) any later version.
**
** This library 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
** Lesser General Public License for more details.
**
** You should have received a copy of the GNU Lesser General Public
** License along with this library; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
 
namespace jmmcg { namespace LIBJMMCG_VER_NAMESPACE { namespace singleton {
 
   /// A so-called "Meyers" singleton.
   /**
      Note that this implementation specifically leaks, and does not clean up, even at atexit(), any resource it allocates.
      Based upon the "Meyers Singleton" from [1], that reference gives full details of the undefined & implementation-defined "features" of this type of singleton.
 
      [1] "Modern C++ Design" by A. Alexandrescu, Chapter 6 "Implementing Singletons", page 133
   */
   template<class V>
   struct leaked_meyers {
      typedef V element_type; ///< The type of the object "managed".
      typedef void argument_type;
      typedef argument_type first_argument_type;
      typedef element_type result_type;
 
      /// Obtain the unique instance of the object.
      /**
         \return The unique instance of the object, initialised and allocated upon the heap, upon first calling, assuming sufficient resources exist.
      */
      static element_type & instance() noexcept(false) {
         static element_type * const val=new element_type();
         return *val;
      }
   };
 
} } }
 
#endif