// Copyright (c) 1997-2000  Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v5.6.1/Nef_2/include/CGAL/Nef_2/geninfo.h $
// $Id: geninfo.h 98e4718 2021-08-26T11:33:39+02:00 Sébastien Loriot
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Michael Seel <seel@mpi-sb.mpg.de>

#ifndef CGAL_NEF_2_GENINFO_H
#define CGAL_NEF_2_GENINFO_H

#include <CGAL/license/Nef_2.h>

#define CGAL_DEPRECATED_HEADER "<CGAL/Nef_2/geninfo.h>"
#define CGAL_DEPRECATED_MESSAGE_DETAILS \
  "Something like boost::any or boost::variant should be used instead."
#include <CGAL/Installation/internal/deprecation_warning.h>

#include <CGAL/config.h>
#include <memory>

/*{\Moptions outfile=geninfo.man}*/
/*{\Moptions constref=yes}*/
/*{\Manpage {geninfo} {T} {Information association via GenPtr} {}}*/

template <typename T>
struct geninfo {
  typedef void* GenPtr;

/*{\Mdefinition |\Mname| encapsulates information association via
generic pointers of type |GenPtr (=void*)|. An object |t| of type |T|
is stored directly in a variable |p| of type |GenPtr| if |sizeof(T)|
is not larger than |sizeof(GenPtr)| (also called word size). Otherwise
|t| is allocated on the heap and referenced via |p|. This class
encapsulates the technicalities, however the user always has to obey
the order of its usage: |create|-|access/const_access|-|clear|. On
misuse memory problems occur.}*/

/*{\Moperations 2 1}*/

  #ifdef CGAL_USE_FORMER_GENINFO
  static void create(GenPtr& p)
  /*{\Mstatic create a slot for an object of type |T| referenced
    via |p|.}*/
  { if (sizeof(T) <= sizeof(GenPtr)) new((void*)(&p)) T;
    if (sizeof(T) >  sizeof(GenPtr)) p = (GenPtr) new T;
  }

  static T& access(GenPtr& p)
  /*{\Mstatic access an object of type |T| via |p|.
    \precond |p| was initialized via |create| and was not cleared
    via |clear|.}*/
  { if (sizeof(T) <= sizeof(GenPtr)) return *(T*)(&p);
    else                             return *(T*)p;
  }

  static const T& const_access(const GenPtr& p)
  /*{\Mstatic read-only access of an object of type |T| via |p|.
    \precond |p| was initialized via |create| and was not cleared
    via |clear|.}*/
  { if (sizeof(T) <= sizeof(GenPtr)) return *(const T*)(&p);
    else                             return *(const T*)p;
  }

  static void clear(GenPtr& p)
  /*{\Mstatic clear the memory used for the object of type |T| via
     |p|. \precond |p| was initialized via |create|.}*/
  { if (sizeof(T) <= sizeof(GenPtr)) ((T*)(&p))->~T();
    if (sizeof(T) >  sizeof(GenPtr)) delete (T*) p;
    p=0;
  }
  #else //CGAL_USE_FORMER_GENINFO
  static void create(GenPtr& p)  { p = (GenPtr) new T; }
  static T& access(GenPtr& p)  { return *(T*)p;  }
  static const T& const_access(const GenPtr& p)
  { return *(const T*)p;   }
  static void clear(GenPtr& p){
    delete (T*) p;
    p=0;
  }
  #endif  //CGAL_USE_FORMER_GENINFO

};

/*{\Mexample In the first example we store a pair of boolean values
which normally fit into one word. Thus there will no heap allocation
take place.
\begin{Mverb}
  struct A { bool a,b };
  GenPtr a;
  geninfo<A>::create(a);
  A& a_access = geninfo<A>::access(a);
  geninfo<A>::clear(a);
\end{Mverb}
The second example uses the heap scheme as two longs do not fit into
one word.
\begin{Mverb}
  struct B { long a,b };
  GenPtr b;
  geninfo<B>::create(b);
  B& b_access = geninfo<B>::access(b);
  geninfo<B>::clear(b);
\end{Mverb}
Note that usage of the scheme takes away with the actual check for the
type size. Even more important this size might depend on the platform
which is used to compile the code and thus the scheme enables platform
independent programming.}*/

#endif //GENINFO_H

