From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
To: alex@baretta.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Protected methods
Date: Thu, 20 Jul 2000 09:46:22 +0900 [thread overview]
Message-ID: <20000720094622J.garrigue@kurims.kyoto-u.ac.jp> (raw)
In-Reply-To: <3D37E364.5060607@baretta.com>
From: Alessandro Baretta <alex@baretta.com>
> > Actually, this seems perfectly practical.
> > If you have some good reason to "protect" a method, you can do it
> > cleanly.
>
> I would not call adding a fake type a clean solution. It's
> not idiomatic. A "protected" keyword is cleaner and easier
> to handle. Although it might be very tricky to implement in
> a language with type inference.
Actually, this is just an alternative model for protection:
give all your clients the key, and don't give it to other people.
This makes sense. The key can be a dummy only because the type system
guarantees that you cannot forge its type.
The problem with a "protected" keyword is that it should be given a
semantics. Since an object type is structural (does not belong to a
specific module), this is unclear how you can define where a protected
method should be accessible.
In practice, I probably won't do it that way, but this would require a
deeper knowledge of your problem.
For instance, if you want to show an internal state to a limited
number of clients, you can just have a method returning this state
with an abstract type. That's certainly more natural.
> How about the following pseudocode? Is it sensible/viable?
>
> let module M : sig
> class type public = object <public_methods> end
> val make_public : unit -> public
> end = struct
> class type public = object <public_methods> end
> class protectd =
> object (self : #public)
> <public_methods>
> <protected_methods>
> end
> let make_public () -> (new protected :> public)
> end
>
> If this a working alternative, I would prefer over both the
> protector type and the protected keyword: clean, simple, and
> idiomatic.
This is both sensible and viable.
The only weakness is that you won't be able to inherit from the public
version of your class, since it is not a class but only a type.
If you need to inherit, you should also export the protected version,
and make sure that all your constructors apply a similar coercion to
hide protected methods.
This inheritance problem is the only reason I didn't suggest this
approach first, but it is certainly simpler.
Jacques Garrigue
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next prev parent reply other threads:[~2002-07-20 0:46 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-07-18 10:42 Alessandro Baretta
2002-07-18 11:01 ` Gerd Stolpmann
2002-07-18 11:44 ` Alessandro Baretta
2002-07-19 8:50 ` Jacques Garrigue
2002-07-19 10:01 ` Alessandro Baretta
2000-07-20 0:46 ` Jacques Garrigue [this message]
2002-07-20 7:41 ` Alessandro Baretta
2002-07-20 1:31 ` Jacques Garrigue
2002-07-20 7:48 ` Alessandro Baretta
2002-07-20 22:48 ` Dmitry Bely
2002-07-20 23:08 ` Brian Smith
2002-07-22 3:37 ` OCaml's OO design " Jacques Garrigue
2002-07-22 4:20 ` John Prevost
2002-07-20 23:54 ` Alessandro Baretta
2002-07-21 7:52 ` Dmitry Bely
2002-07-21 13:14 ` Alessandro Baretta
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