I am sure there are thousands of better alternatives to this approach, but I was wondering whether
there is an elegant way to make a class method call another class method within the same ancestor
level, instead of going for the youngest offspring.

Example:

TParentClass = class
protected
  class procedure DoSomething; virtual;
  class procedure DoSomethingExtra; virtual;
end;

TChildClass = class(TParentClass)
protected
  class procedure DoSomething; override;
  class procedure DoSomethingExtra; override;
end;

Code:

procedure TParentClass.DoSomething;
begin
  DoSomethingExtra
end;

procedure TChildClass.DoSomething;
begin
  inherited;
  // non-relevant extra code
end;

How can I easily achieve that when the inherited part in TChildClass.DoSomething is executed, the
DoSomethingExtra method call in TParentClass.DoSomething calls the TParentClass.DoSomethingExtra
method and not TChildClass.DoSomethingExtra.

I know I can resolve this by, for instance, putting some of the code in the private part, or by
carrying out class checking in the inherited DoSomethingExtra method, but I was wondering whether
there is a way to force a class method call to remain within its own class?

Many thanks.

Cheers,
Dom

-snip-

The solution is to simple make DoSomethingextra static, not virtual.

Peter Below (TeamB)  100113.1...@compuserve.com)
No e-mail responses, please, unless explicitly requested!

"Peter Below (TeamB)" <100113.1...@compuXXserve.com>
 > The solution is to simple make DoSomethingextra static, not virtual.

Many thanks for your reply.
I forgot to mention, however, that DoSomethingExtra implements (descends from and implements) an
abstract method, hence I can't make it static.

Dom

"Dominique Willems" <do...@compuserve.com> wrote
Bull. Ignore my ramblings and many thanks for the assistance! :)

Cheers,
Dom

In that case, do not override DoSomethingExtra in the derived class, only
in the parent class (which descends from the abstract class, I hope).
--
Rudy Velthuis (Team JEDI)
http://delphi-jedi.org

Wait... we want to know to what conclusion you have come.

And commercials for Bull should go to thirdpartytools. <g>
--
Rudy Velthuis (Team JEDI)
http://delphi-jedi.org

"Rudy Velthuis (Team JEDI)" <rvelth...@gmx.de>
It's a mess at the moment, Rudy. I posted an extreme simplification of the problem and am currently
gathering the courage to construct a complete example of what I am doing. It involves dynamically
created class references, and with the static solution proposed the methods being called fall back
onto the abstract ancestor.

Trying to focus my mind for a change, so that I can post something clear.

Thanks!
Dom

"Rudy Velthuis (Team JEDI)" <rvelth...@gmx.de>

It's a mess at the moment, Rudy. I posted an extreme simplification of the problem and am currently
gathering the courage to construct a complete example of what I am doing. It involves dynamically
created class references, and with the static solution proposed the methods being called fall back
onto the abstract ancestor.

Trying to focus my mind for a change, so that I can post something clear.

Thanks!
Dom

Here's the deal:

TGrandFatherClass = class
  class procedure DoSomething; virtual; abstract;
  class procedure DoSomethingExtra; virtual; abstract;
end;

TParentClass = class(TGrandFatherClass)
protected
  class procedure DoSomething; override;
  class procedure DoSomethingExtra; override;
end;

TChildClass = class(TParentClass)
protected
  class procedure DoSomething; override;
  class procedure DoSomethingExtra; override;
end;

Code:

var
  Obj: TGrandFatherClass;

procedure SomeIrrelevantClass.SomeProcedure;
begin
  Obj := TChildClass.Create;
  Obj.DoSomething  ----> executes TChildClass.DoSomething, then TParentClass.DoSomething,
                                    then TChildClass.DoSomethingExtra (which I don't want; I want it
to
                                    execute TParentClass.DoSomethingExtra)...
end;

procedure TParentClass.DoSomething;
begin
  DoSomethingExtra
end;

procedure TParentClass.DoSomethingExtra;
begin
  // Do something useful
end;

procedure TChildClass.DoSomething;
begin
  inherited;
  // non-relevant extra code
end;

procedure TChildClass.DoSomethingExtra;
begin
  inherited;
  // do something useful, but specific to TChildClass
end;

I hope I haven't over-simplified this time.

Thanks,
Dom

Your TChildClass.DoSomethingExtra seems to be made to be called by
TChildClass methods only, so why put it in the inheritance tree? Why not
just create a new method that calls "inherited DoSomethingExtra" instead?

See below:

Why not get rid of TChildClass.DoSomethingExtra, and create:

procedure TChildClass.DoSomethingEvenMoreExtra; // non-virtual!
begin
  inherited DoSomethingExtra; // explicit call of ancestor method.
  // do something useful, but specific to TChildClass
end;

This way, a call to DoSomethingExtra will always call
TParentClass.DoSomethingExtra, both from the parent and the child class.

IOW: just stop inheritance at the father class, and go on with a new
static method for the child class. This can call "inherited
DoSomethingExtra" explicitly.

--
Rudy Velthuis (Team JEDI)
http://delphi-jedi.org

"Rudy Velthuis (Team JEDI)" <rvelth...@gmx.de>

Well, TChildClass.DoSomethingExtra is actually a method that is also called from other classes.
These other classes assume the existence of a DoSomethingExtra method as defined in
TGrandFatherClass.

If only there existed a modifier like "this" that could force the method call to occur inside the
current method's class. Something like

"this DoSomethingExtra" would be of great use to me now. :)

Thanks,
Dom