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Overriding◄╣

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► KB ► To/From Guides ► ObjectPAL ► Language Details

Overriding (Cross Ref > Language Details)

By Mike Prestwood

ObjectPAL versus Delphi Prism: A side by side comparison between ObjectPAL and Delphi Prism.

OOP Details

More object oriented (OO) stuff.

Overriding

[Other Languages]

General Info: Method Overriding

Where you define or implement a virtual method in a parent class and then replace it in a descendant class.

When you decide to declare a method as virtual, you are giving permission to derived classes to extend and override the method with their own implementation. You can have the extended method call the parent method's code too.

In most OO languages you can also choose to hide a parent method. When you introduce a new implementation of the same named method with the same signature without overriding, you are hiding the parent method.

ObjectPAL: Not Supported

Delphi Prism: virtual, override

Same as Delphi. In Prism, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

Use final to prevent further extending of a member and Sealed to prevent all members of a class from further extension.

Syntax Example:

Robot = class(System.Object)
public
  method Speak; virtual;
end;

Cyborg = class(Robot)
public
  method Speak; override;
end;

Delphi Prism Overriding (virtual, override)