/* 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> template <typename T2>Stack<T>& Stack<T>::operator= (Stack<T2> const& op2){    if ((void*)this == (void*)&op2) {    // assignment to itself?        return *this;    }    Stack<T2> tmp(op2);              // create a copy of the assigned stack    elems.clear();                   // remove existing elements    while (!tmp.empty()) {           // copy all elements        elems.push_front(tmp.top());        tmp.pop();    }    return *this;}