Explicit programmer-specified polymorphism

You can write f() such that it can operate on multiple types in any of the following ways:

• Preprocessing:

  #define f(X)((X)+=2)// (note: in real code, use a longer uppercase name for a macro!)

• Overloading:

  void f(int& x){
         x +=2;}void f(double& x){
         x +=2;}

• Templates:

  template
        
         void f(T& x){
         x +=2;}
        

• Virtual dispatch:

  structBase{
        virtualBase&operator+=(int)=0;};struct X :Base{
            X(int n): n_(n){
        }    X&operator+=(int n){
         n_ += n;return*this;}int n_;};struct Y :Base{
            Y(double n): n_(n){
        }    Y&operator+=(int n){
         n_ += n;return*this;}double n_;};void f(Base& x){
         x +=2;}// run-time polymorphic dispatch