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[Caml-list] a design problem requiring downcasting? (long)
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Date: 2002-09-30 (09:44)
From: Alessandro Baretta <alex@b...>
Subject: Re: [Caml-list] a design problem requiring downcasting? (long)

Michael Vanier wrote:
> I'm not sure.  All the approaches I've seen in ocaml seem incredibly heavy
> compared with RTTI in java (and/or more brittle).  I'm not sure about your
> approach, though (it looks pretty light).  Thanks for the suggestion!

You are very welcome ;)

> Here is a question for the language designers: is there a technical reason
> why RTTI can't be done easily in the ocaml object system?  Or is the lack
> of RTTI more of a "moral" issue?  Or is it just due to not enough time to
> put in all the features one would like?  I can imagine that the fact that
> subtyping is implicit for any class that implements the methods of a
> superclass might make RTTI very tricky to implement cleanly in a general
> way.  

I don't think there will be any Caml preachers prophesyzing 
your doom for having desired RTTI. I just have a feeling it 
does not fit in cleanly with the type system.

> It's too bad we can't all roll our own object systems for ocaml ;-)
> Mike

Who says you can't? Pick up CamlP4 and write preprocessing 
code adding your favorite flavor of RTTI to your your 
classes. You might very well automate the generation of 
polymorphic-variant-RTTI-tagging object creation 
functions--my flavor of RTTI--or any other flavor you like 
best. One might even come up with a syntax extension 
supporting some form of double-dispatch polymorphism. But, 
to my great dishonor, I'm still not a CamlP4 guru, so I'll 
leave this to others.


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