Re: subtyping and inheritance

[Markus Mottl <mottl@miss.wu-wien.ac.at>]

> On Mon, Jan 25, 1999 at 01:08:30AM +0100, Markus Mottl wrote:
> [...]
> > So far it seems that things would be unsafe with covariance. But now,
> > Castagna answers my (former) question, whether making "reappear" methods
> > from ancestors would be safe: it is...
> > 
> > The paper looked difficult at first, but turned out to be surprisingly
> > easy to read: Castagna makes the theorie very intuitively clear with his
> > examples of classes "2DPoint" and "3DPoint" and how methods are chosen
> > in the different models.
> > 
> > The record based method (as found in OCAML - the object (record)
> > determines, which method is selected, arguments are not considered)
> > can be obviously extended to support covariance.
> 
> However, it is not possible to apply this extension to Ocaml.  Indeed,
> it requires that methods are chosen depending on the dynamic type of
> their arguments.  But this information is not available in Ocaml.
> There are also difficulties for type inference.

What a pity...

At least we know now, that design questions have to be solved quite
differently in OCAML than in some other OO-languages.

Regards,
Markus

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl