function-erasure.hpp

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/*
  FUNCTION-ERASURE.hpp  -  wrapping a functor object for inline storage while hiding the signature

  Copyright (C)         Lumiera.org
    2009,               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 LIB_META_FUNCTION_ERASURE_H
#define LIB_META_FUNCTION_ERASURE_H

#include "lib/util.hpp"
#include "lib/error.hpp"
#include "lib/opaque-holder.hpp"

#include <functional>


namespace lib {
namespace meta{
  
  using std::function;
  using util::unConst;
  
  
  
  /**************************************************/
  template<class FH>
  struct FunErasure
    : FH
    {
      template<typename FUN>
      FunErasure (FUN const& functor)
        : FH(functor)
        { }
      
      friend bool
      operator!= (FunErasure const& fer1, FunErasure const& fer2)
        {
          return not (fer1==fer2);  // use equality defined by FH
        }
    };
  
  
  /* ====== Policy classes ====== */
  
  typedef function<void(void)> FunVoid;
  typedef lib::InPlaceAnyHolder< sizeof(FunVoid)                       // same size for all function objects 
                               , lib::InPlaceAnyHolder_unrelatedTypes  // no common base class!
                               > FunHolder;
  typedef lib::InPlaceAnyHolder< sizeof(void*) 
                               , lib::InPlaceAnyHolder_unrelatedTypes
                               > FunPtrHolder;
  
                               
  class StoreFunction
    : public FunHolder
    {
    public:
      template<typename SIG>
      StoreFunction (SIG& fun)
        : FunHolder(function<SIG>(fun))
        { }
      
      template<typename SIG>
      StoreFunction (function<SIG> const& fun)
        : FunHolder(fun)
        { }
      
      template<typename SIG>
      function<SIG>&
      getFun ()  const
        {
          return get<function<SIG>>();
        }
    };
  
  
  class StoreFunPtr
    : public FunPtrHolder
    {
    public:
      template<typename SIG>
      StoreFunPtr (SIG& fun)
        : FunPtrHolder(&fun)
        { }
      
      template<typename SIG>
      StoreFunPtr (SIG *fun)
        : FunPtrHolder(fun)
        { }
      
      template<typename SIG>
      SIG&
      getFun ()  const
        {
          SIG *fun = get<SIG*>();
          REQUIRE (fun);
          return *fun;
        }
    };
  
  
  class StoreUncheckedFunPtr
    {
      void *funP_;
      
    public:
      template<typename SIG>
      StoreUncheckedFunPtr (SIG& fun)
        {
          funP_ = reinterpret_cast<void*> (&fun);
        }
      template<typename SIG>
      StoreUncheckedFunPtr (SIG *fun)
        {
          funP_ = reinterpret_cast<void*> (fun);
        }
      
      template<typename SIG>
      SIG&
      getFun ()
        {
          return *reinterpret_cast<SIG*> (funP_);
        }
      
      
      explicit operator bool() const { return funP_; }
      bool isValid()           const { return funP_; }
      
    };
  
  
  
  
}} // namespace lib::meta
#endif