Title: Hacking a final method in Delphi 8
Question: Delphi 8 provides the facility to declare a method of a class as final, but if you really want to override it?
Answer:
In Delphi8 the final keyword is introduced, it can be used to specify that a method in a class cannot be reintroduced, in other words, it can be used to break a polymorphic chain of methods.
Why would you want to do that?, one reason is to allow the JITer to optimise method calls, other can be that you dont want anybody else to extend the functionallity of your code.
Nevertheless, using a dirty hack you can continue to override a final method, supose you have the following code:
type
TBaseClass = class
public
procedure DoSomething;virtual;
end;
TDerivedClass = class(TBaseClass)
public
procedure DoSomething;override;final;
end;
Now, since DoSomething is final, if you declare
TAnotherClass = class(TDerivedClass)
public
procedure DoSomething;override;
end;
the compiler gives you the following error:
[Error] Project1.dpr(21): Cannot override a final method
If you modify the code for TAnotherClass as follows:
TAnotherClass = class(TDerivedClass)
public
procedure DoSomething;reintroduce;virtual;
end;
You can still call the inherited method like this:
procedure TAnotherClass.DoSomething;
begin
inherited;
// your code here
end;
Enjoy.