/* The following code example is taken from the book * "C++ Templates - The Complete Guide" * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002 * * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002. * Permission to copy, use, modify, sell and distribute this software * is granted provided this copyright notice appears in all copies. * This software is provided "as is" without express or implied * warranty, and with no claim as to its suitability for any purpose. */template <typename T>class Holder {  // previously defined members  //...  public:    Holder (Trule<T> const& t) {        ptr = t.ptr;        const_cast<Trule<T>&>(t).ptr = 0;    }    Holder<T>& operator= (Trule<T> const& t) {        delete ptr;        ptr = t.ptr;        const_cast<Trule<T>&>(t).ptr = 0;        return *this;    }};