From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
To: andrew@absentis.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Passing self to a new object
Date: Mon, 29 Oct 2001 18:02:07 +0900 [thread overview]
Message-ID: <20011029180207D.garrigue@kurims.kyoto-u.ac.jp> (raw)
In-Reply-To: <20011028155625.A1303@alba.sw>
From: Andrew Lawson <andrew@absentis.com>
> I'm writing a gui program where the callback for a button
> creates a new object (also a gui) and needs to pass it a reference to
> itself in order that the new object can contact the original for
> information. The classes look something like this;
>
> class xyz =
> let top = ... in
> let ... = ... in
> object (self)
> method btnNew = ... ~command:(fun () = new abc self) top in
> ...
> ...
> end
>
> and abc (parent:xyz) =
> object (self)
> var myparent = parent
> ...
> end
>
>My error is;
> .....
> Self type cannot escape its class
You've bumped into a painful quirk of ocaml's object system: self's
type is not xyz, and must be handled with care.
(By the way, your program seemed strange, since you were using self
and abc before defining them, but I suppose it was a copy error, and I
corrected it.)
The general solution to this is to first define a class type:
class type xyz_t = object ('self)
method
btnNew : ...
...
end
Then change the code in btnNew to
new abc (self :> xyz_t)
Remark that making xyz_t exact may be a bit lengthy, but you may leave
out methods you don't need to call from abc.
Hope this helps,
Jacques Garrigue
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next prev parent reply other threads:[~2001-10-29 9:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-10-28 15:56 Andrew Lawson
2001-10-29 9:02 ` Jacques Garrigue [this message]
2001-10-29 20:30 ` Andrew Lawson
2001-10-30 8:09 ` Jacques Garrigue
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