Overriding

In a derived class, you can override inherited methods to change their behavior. When overriding a method, the declaration must match exactly, including the argument names and types and the return type. (Ultra Fractal supports covariant return types, so if the return type is a class, it can also be a descendant of the return type of the inherited method.)

In the overridden method, you can call the inherited method using the ancestor class name and the member operator. Here is an example where the Derived class overrides a method inherited from Base, and calls the inherited method:

class Base {
  int func test()
    return 3
  endfunc
}

class Derived(Base) {
  int func test()
    return Base.test() * 2
  endfunc
}

Ultra Fractal always uses virtual method dispatching for all methods. This means that when you call a method on an object, the actual type of the object is determined and the method for that object type is called. This matters when using inheritance and method overriding:

Base b = new Base
print(b.test())  ; Prints 3
Derived d = new Derived
print(d.test())  ; Prints 6
; Test virtual method dispatching
Base x = b
print(x.test())  ; Prints 3
x = d
print(x.test())  ; Prints 6

When x.test() is executed, the actual type of x is determined and the corresponding method is called. In the first case, the actual type of x is Base, so Base.test() is called, which returns 3. In the second case, Derived.test() is called because the actual type of x is Derived, even though x is declared as a reference to Base. This behavior is extremely useful with plug-in parameters.

Note: Unlike methods, member variables are never overridden. If you declare a variable in a derived class with the same name as a variable in the ancestor class, the new variable will exist in addition to the (now hidden) inherited variable. Because the new variable doesn't have any relationship with the inherited variable, it is legal for it to be of a different type. Generally, declaring variables with the same name as inherited variables is not recommended since it can easily lead to confusion.

Next: Constructors

See Also
Classes
Inheritance
Methods