Question

Consider the following snippet:

struct ObjectInterface {     virtual ~ObjectInterface() {}     virtual void Print(std::ostream& target) const = 0; };  struct Foo : ObjectInterface {     virtual void Print(std::ostream& target) const     {         target << 'Foo';     } };  struct Bar : ObjectInterface {     virtual void Print(std::ostream& target) const     {         target << 'Bar';     } }; 

Is there any way to change Print in ObjectInterface to the standard ‘std::ostream& operator<<‘-type of output? I can’t make it work.

EDIT: I’m basically trying to figure out if I can make friend work with virtual.

Answer 1

You need a free function:

ostream & operator << ( ostream & os, const ObjectInterface & oi ) {     oi.Print( os );     return os; }