objects with variant part

[Kays]

Why can't objects have variant parts?

Code: Pascal  [Select][+][-]

1. myObj = object
2.                 case foo: byte of
3.                         …
4.         end;

works as a record only. I thought “Objects should be treated as a special kind of record.” (Chapter on “objects” in the reference manual)

[Leledumbo]

Why can't objects have variant parts?

I can't really think of any technical reason, so I guess it's down to compatibility only, as object can have a field of type variant record, which should be the same in the end (minus the longer access).

[Thaddy]

It is perfectly possible (and the entry point will be the same for object and record.)
The correct syntax however is to declare a record inside the object, like:

Code: Pascal  [Select][+][-]

1. program program1;
2. {$ifdef fpc}{$mode delphi}{$H+}{$endif}
3. type
4.   foo = object
5.     bar:record
6.     case EyeColor: (Red, Green, Blue, Brown) of
7.       Red, Green : (WearsGlasses: Boolean);
8.       Blue, Brown: (LengthOfLashes: Integer);
9.     end;
10.  end;
11. begin
12. end.

The record can subsequently contain variant parts if required as you see here.
Contrived example, any use for it?  (Parts of it are from the GNU Pascal manual...)

[Kays]

[…]I can't really think of any technical reason, so I guess it's down to compatibility only, as object can have a field of type variant record, which should be the same in the end (minus the longer access).

It is perfectly possible (and the entry point will be the same for object and record.)
The correct syntax however is to declare a record inside the object, like:[…]

That introduces another level I wanted to avoid.

Code: Pascal  [Select][+][-]

1. var
2.         subject: foo;
3. begin
4.         subject.bar.eyeColor := red;
5.         // but simply
6.         //subject.eyeColor := red;
7.         // does not work
8. end.

so a variant part per se can't be a member of an object.

It'd been nice, if I could write myObject.convertToBlub(), but I'm OK with convertToBlub(myRecord). I really don't like to have longer access paths.

[Thaddy]

Kai, it is not another level of indirection. You did not use  the correct syntax. But syntax can be discussed on the mailing list.... (Good luck!)
Also note that work is being done - in trunk+ -  on the subject of default properties.... That would solve it...

[Martin_fr]

If you just need procedures, then use advanced records (search forum / wiki)

"object" is only needed, if you want a record like structure with inheritance.