/* The following code example is taken from the book * "The C++ Standard Library - A Tutorial and Reference" * by Nicolai M. Josuttis, Addison-Wesley, 1999 * * (C) Copyright Nicolai M. Josuttis 1999. * 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. */#include <functional>/* class for the compose_f_gx adapter */template <class OP1, class OP2>class compose_f_gx_t : public std::unary_function<typename OP2::argument_type,                              typename OP1::result_type>{  private:    OP1 op1;    // process: op1(op2(x))    OP2 op2;  public:    // constructor    compose_f_gx_t(const OP1& o1, const OP2& o2)     : op1(o1), op2(o2) {    }    // function call    typename OP1::result_type    operator()(const typename OP2::argument_type& x) const {        return op1(op2(x));    }};/* convenience function for the compose_f_gx adapter */template <class OP1, class OP2>inline compose_f_gx_t<OP1,OP2>compose_f_gx (const OP1& o1, const OP2& o2) {    return compose_f_gx_t<OP1,OP2>(o1,o2);}