wrapper.h

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// -*- C++ -*-
// Little library of copy-on-write wrappers
// Copyright (C) 2007- Leon Bottou


// 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 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., 59 Temple Place, Suite 330, Boston, MA 02111, USA



// $Id: wrapper.h,v 1.8 2007/10/02 20:40:06 cvs Exp $


#ifndef WRAPPER_H
#define WRAPPER_H 1


template <class Rep> 
class Wrapper
{
private:
  Rep *q;
  Rep *ref(Rep *q) { q->refcount++; return q; }
  void deref(Rep *q) { if (! --(q->refcount)) delete q; }
  
public:
  Wrapper() 
    : q(new Rep) { q->refcount = 1; }
  Wrapper(Rep *rep)
    : q(rep) { q->refcount = 1; }
  Wrapper(const Wrapper<Rep> &other) 
    : q(ref(other.q)) {}
  ~Wrapper() 
  { deref(q); }
  Wrapper& operator=(const Wrapper<Rep> &other) 
  { Rep *p = q; q = ref(other.q); deref(p); return *this; }
  void detach() 
  { if (q->refcount > 1) { deref(q); q=q->copy(); q->refcount=1; } }
  Rep *rep() const
  { return q; }
};



// Recommended usage
//
// #include <cstdlib>
// #include <cstring>
// 
// class String
// {
// private:
//
//   struct Rep
//   {
//     int refcount;
//     int length;
//     char *data;
//     Rep(const char *s, int l)
//       : length(len), data(new char[l+1]) 
//       { ::memcpy(data, s, l);  data[len] = 0; }
//     Rep *copy()
//       { return new StringRep(data, length); }
//   };
//
//   Wrapper<Rep> w;
//   Rep *rep() { return w.rep(); }
//   const Rep *rep() const { return w.rep(); }
//     
// public:
//   String(const char *s, int l)
//     : w(new Rep(s,l)) {}
//   String(const char *s)
//     : w(new Rep(s,::strlen(s))) {}
// 
//   // function that do not mutate
//   int size() const { return rep()->length; }
//   operator const char*() const { return rep()->data; }
//   char operator[](int i) const { return rep()->data[i]; }
//   
//   // functions that perform a mutation
//   void set(int i, char c) { w.detach(); rep()->data[i] = c; }
// }
// 



#endif



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