/* Code for exercise 14.10. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*/#include <stdio.h>struct Callback {   virtual void operator()() = 0;   virtual void operator()() const = 0;};template<void (*PF)()>struct CallbackFunction: Callback {   virtual void operator()() { PF(); }   virtual void operator()() const { PF(); }};template<typename T, void (T::*MF)()>struct ObjectCallback: Callback {   ObjectCallback(T &object): object_(object) {}   virtual void operator()() { (object_.*MF)(); }   virtual void operator()() const { (object_.*MF)(); }private:   T &object_;};void a() { printf("Hello\n"); }void b() { printf("World!\n"); }struct X {   X(char const *p, char const *q): p_(p), q_(q) {}   void f() { printf("%s\n", p_); }   void g() { printf("%s\n", q_); }private:   char const *p_, *q_;};void greet(Callback const &first, Callback const &second) {   first();   second();}int main() {   greet(CallbackFunction<&a>(), CallbackFunction<&b>());   X x("Hello", "Class!");   greet(ObjectCallback<X, &X::f>(x), ObjectCallback<X, &X::g>(x));}