Polymorphism

• Hiding provides compile-time polymorphism
• Almost always, this is not what is desired, and should be avoided!
• Want to be able to choose the class type of an object at run-time
• Suppose we want to write a function such as:
  

  void use(Employee* e) {
  e->getEmployeeType();
  }

  
  and then call it using Employee, Empowered, Manager objects:
  

  use(&e1); // output: Employee
  use(&e2); // output: Employee
  use(&e3); // output: Employee

• As far as use() is concerned, the pointers are all of Employee type, so wrong method is called

Run-time polymorphism can be obtained by declaring the relevant methods as virtual

class Employee {
...
virtual void getEmployeeType(void);
...
};

class Empowered : public Employee {
...
virtual void getEmployeeType(void);
...
};

class Manager : public Empowered {
...
virtual void getEmployeeType(void);
...
};

use(&e1); // output: Employee
use(&e2); // output: Empowered
use(&e3); // output: Manager