From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
To: nadji@noos.fr
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] polymorphic method question
Date: Thu, 22 Aug 2002 07:57:44 +0900 [thread overview]
Message-ID: <20020822075744N.garrigue@kurims.kyoto-u.ac.jp> (raw)
In-Reply-To: <3D640AF1.C24688A@noos.fr>
From: nadji@noos.fr
> I am puzzled by this behaviour, can a guru explain me ?
> I have two classes
[...]
> I want to do a class gentoto :
> class gentoto = object
> method gen : 'a . 'a -> 'a basic =
> fun x -> (new toto x :> 'a basic )
> end;;
> But the compiler complains that :
> Characters 64-98:
> fun x -> (new toto x :> 'a basic )
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This method has type 'a -> 'a basic which is less general than
> 'b. 'b -> 'b basic
>
> ... but if I do :
> let newtotoasbasic x = (new toto x :> 'a basic );;
[...]
> The compiler agrees with me ...
> What is wrong with the first declaration ?
There is a problem with the scoping of named type variables in the
language, which makes them incompatible with polymorphic methods.
You can solve this by using anonymous variables:
# class gentoto = object
method gen : 'a . 'a -> 'a basic =
fun x -> (new toto x :> _ basic)
end;;
class gentoto : object method gen : 'a -> 'a basic end
Jacques Garrigue
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next prev parent reply other threads:[~2002-08-21 22:58 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-21 21:49 nadji
2002-08-21 22:57 ` Jacques Garrigue [this message]
2006-07-10 19:21 Polymorphic " brogoff
2006-07-10 20:05 ` [Caml-list] " Richard Jones
2006-07-10 23:25 ` brogoff
2006-07-11 2:24 ` skaller
2006-07-11 4:56 ` brogoff
2006-07-11 2:09 ` Jacques Garrigue
2006-07-11 5:22 ` brogoff
2006-07-11 7:32 ` Jacques Garrigue
2006-07-11 18:20 ` brogoff
2006-07-12 0:37 ` Jacques Garrigue
2006-07-12 19:26 ` brogoff
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