type-handler.hpp

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/*
  TYPE-HANDLER.hpp  -  a functor pair for setup and destruction

  Copyright (C)         Lumiera.org
    2011,               Hermann Vosseler <Ichthyostega@web.de>

  This program 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.

  This program 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 this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#ifndef STEAM_ENGINE_TYPE_HANDLER_H
#define STEAM_ENGINE_TYPE_HANDLER_H


#include "lib/error.hpp"
#include "lib/hash-value.h"

#include <functional>
#include <boost/functional/hash.hpp>


namespace steam {
namespace engine {
  
  using lib::HashVal;
  using std::bind;
  using std::function;
  using std::placeholders::_1;
  
  namespace error = lumiera::error;
  
  
  namespace { // (optional) helpers to build an object embedded into a buffer...
    
    template<class X>
    inline void
    buildIntoBuffer (void* storageBuffer)
    {
      new(storageBuffer) X();
    }
    
    template<class X, typename A1>
    inline void
    buildIntoBuffer_A1 (void* storageBuffer, A1 arg1)
    {
      new(storageBuffer) X(arg1);
    }
    
    template<class X>
    inline void
    destroyInBuffer (void* storageBuffer)
    {
      X* embedded = static_cast<X*> (storageBuffer);
      embedded->~X();
    }
    
    template<typename CTOR, typename DTOR>
    inline HashVal
    deriveCombinedTypeIdenity()
    {
      HashVal hash{0};
      boost::hash_combine (hash, typeid(CTOR).hash_code());
      boost::hash_combine (hash, typeid(DTOR).hash_code());
      return hash;
    }
  }//(End)placement-new helpers
  
  
  
  struct TypeHandler
    {
      typedef function<void(void*)> DoInBuffer;
      
      DoInBuffer createAttached;
      DoInBuffer destroyAttached;
      HashVal identity;
      
      TypeHandler()
        : createAttached()
        , destroyAttached()
        , identity{0}
        { }
      
      template<typename CTOR, typename DTOR>
      TypeHandler(CTOR ctor, DTOR dtor)
        : createAttached (ctor)
        , destroyAttached (dtor)
        , identity{deriveCombinedTypeIdenity<CTOR,DTOR>()}
        { }
      
      template<class X>
      static TypeHandler
      create ()
        {
          return TypeHandler (buildIntoBuffer<X>, destroyInBuffer<X>);
        }
      
      template<class X, typename A1>
      static TypeHandler
      create (A1 a1)
        {
          return TypeHandler ( bind (buildIntoBuffer_A1<X,A1>, _1, a1)
                             , destroyInBuffer<X>);
        }
      
      bool
      isValid()  const
        {
          return bool(createAttached)
             and bool(destroyAttached);
        }
      
      friend HashVal
      hash_value (TypeHandler const& handler)
      {
        return handler.identity;
      }
      
      friend bool
      operator== (TypeHandler const& left, TypeHandler const& right)
      {
        return (not left.isValid() and not right.isValid())
            || (left.identity == right.identity);
      }
      friend bool
      operator!= (TypeHandler const& left, TypeHandler const& right)
      {
        return not (left == right);
      }
    };
  
  
  
}} // namespace steam::engine
#endif