// (C) Porkolab 2003 // // A.6.18. // Function objects template<class T> class Sum { T res; public: Sum(T i = 0) : res(i) { } // initialize void operator()(T x) { res += x; } // accumulate T result() const { return res; } // return sum }; /* * Usage of a function objects * */ void f(list<double>& ld) { Sum<double> s; s = for_each(ld.begin(),ld.end(),s); // invoke s() for each element of ld cout << "the sum is " << s.result() << '\n'; } template <class Arg, class Res> struct unary_function { typedef Arg argument_type; typedef Res result_type; }; template <class Arg, class Arg2, class Res> struct binary_function { typedef Arg first_argument_type; typedef Arg2 second_argument_type; typedef Res result_type; }; template <class T> struct logical_not : public unary_function<T,bool> { bool operator()(const T& x) const { return !x; } }; template <class T> struct less : public binary_function<T,T,bool> { bool operator()(const T& x, const T& y) const { return x<y; } };