/* 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. */#ifndef TRULE_HPP#define TRULE_HPPtemplate <typename T>class Holder;template <typename T>class Trule {  private:    T* ptr;    // objects to which the trule refers (if any)  public:    // constructor to ensure that a trule is used only as a return type    // to transfer holders from callee to caller!    Trule (Holder<T>& h) {        ptr = h.get();        h.release();    }    // copy constructor    Trule (Trule<T> const& t) {        ptr = t.ptr;        const_cast<Trule<T>&>(t).ptr = 0;    }    // destructor    ~Trule() {         delete ptr;     }  private:    Trule(Trule<T>&);                // discourage use of lvalue trules    Trule<T>& operator= (Trule<T>&); // discourage copy assignment    friend class Holder<T>;};#endif // TRULE_HPP