/* 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, typename A1, typename A2>class A_Subscript {  public:    // constructor initializes references to operands    A_Subscript (A1 const & a, A2 const & b)     : a1(a), a2(b) {    }    // process subscription when value requested    T operator[] (size_t idx) const {        return a1[a2[idx]];    }    T& operator[] (size_t idx) {        return a1[a2[idx]];    }    // size is size of inner array    size_t size() const {        return a2.size();    }  private:    A1 const & a1;    // reference to first operand    A2 const & a2;    // reference to second operand};