Re: What is polymorphism?

Seigfried wrote:


Don't top post. It's considered rude here.

The book is right. C++ implements run-time (or dynamic) polymorphism
through the virtual function mechanism. For instance:

 #include <iostream>

 struct Foo
 {
   virtual void Message() const { std::cout << "Foo::Message()\n"; }
 };

 struct Bar : Foo
 {
   virtual void Message() const { std::cout << "Bar::Message()\n"; }
 };

 void CallMessage( const Foo& foo )
 {
   foo.Message(); // This is the key line
 }

 int main()
 {
   Foo foo;
   Bar bar;
   CallMessage( foo );
   CallMessage( bar );
 }

Note that CallMessage() accepts a reference (it could just as well
accept a pointer, but not an object). That function requests that the
object of type Foo (or a derived type thereof) print its message. Any
object in the hierarchy based at Foo can be passed into that function,
but each can respond to the "message" (i.e. function call) differently
thanks to the virtual function mechanism in C++. This is just what your
book said: Foo and Bar are different (though related) objects that
respond differently to the same message (i.e., invocation of the
virtual function Message()).

Cheers! --M