From: brogoff@speakeasy.net
To: Olivier Andrieu <andrieu@ijm.jussieu.fr>
Cc: onlyclimb <onlyclimb@163.com>, "caml-list@inria.fr" <caml-list@inria.fr>
Subject: Re: [Caml-list] How to throw away oop?
Date: Mon, 9 Dec 2002 10:43:59 -0800 (PST) [thread overview]
Message-ID: <Pine.LNX.4.44.0212091028530.25287-100000@grace.speakeasy.net> (raw)
In-Reply-To: <15860.42055.229312.122122@akasha.ijm.jussieu.fr>
On Mon, 9 Dec 2002, Olivier Andrieu wrote:
> onlyclimb [Monday 9 December 2002] :
> > DNA and Protein can be a subclass of Seq. And in fact there are many
> > kind of sequences , so we can suppose the number of the kind of Seq is
> > infinite. ie. the subclasses of Seq can be infinite. and DNA and
> > Protein are just two of them
>
> Do you really think you'll have to subclass your Seq often ? I mean,
> you have DNA, proteins and this is it (you can add RNA if you want to
> nitpick). In this case, ie when your datatypes are fixed and you're not
> going to extend them, you can simply use a variant type.
In the case of a function like "length", there are certainly a lot of things
which satisfy it. Most of the time, writing Foo.length is OK, but there
are certainly times when it is less clear IMO. It seems what the original
poster misses here isn't so much OOP but overloading, since there is no
late-binding/open-recursion/implementation-inheritance though it turns out
that OCaml's object system gives you something like overloading. I prefer
Olivier's solution in this case
> module DNA =
> type t = ...
> let length = ...
> end
>
> module Protein =
> type t = ...
> let length = ...
> end
>
> and you can build a generic module for functions common in DNA and
> Protein :
>
> module Seq =
> type t =
> | DNA of DNA.t
> | Protein of Protein.t
> let length = function
> | DNA s -> DNA.length s
> | Protein s -> Protein.length s
> end
and, if we had true generics as in GCaml, we could write this
generic length =
DNA.t -> DNA.length
| Protein -> Protein.length
directly without the tagging and untagging. This would be my preferred
solution if it were in the language.
-- Brian
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prev parent reply other threads:[~2002-12-09 18:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-09 21:20 onlyclimb
2002-12-09 13:45 ` Didier Le Botlan
2002-12-09 14:10 ` Olivier Andrieu
2002-12-09 18:43 ` brogoff [this message]
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