[Caml-list] Types of classes (was: Re: "ocaml_beginners"::[] OCaml tutorial)

[Richard Jones <rich@annexia.org>]

On Sun, Jun 15, 2003 at 01:09:44PM +0200, Remi Vanicat wrote:
> Well, I've spot[ted] another mistake :
> 
> http://merjis.com/richj/computers/ocaml/tutorial/ch8.shtml
> 
> Say (about function acting over object) :
> 
> "
> We can force OCaml to be more specific and only allow drain_stack to
> be called on 'a stacks by narrowing the type of the s argument, like
> this: 
> 
> # let drain_stack (s : 'a stack) =
>   while s#size > 0 do
>     ignore (s#pop)
>   done;;
> val drain_stack : 'a stack -> unit = <fun>
> "
> 
> this is not true, the type 'a stack is only an alias for the type :
> 
> < push : 'a -> unit; pop : 'a; peek : 'a; size : int >
> 
> and, as such, drain_stack can be called (for example) with an
> argument of class stack_of_ints, but also on a object of the following
> class :
> 
> class ['a] foo (x : 'a) =
> object
>   method push (y : 'a) = ()
>   method pop = x
>   method peek = x
>   method size = 1
> end


Isn't this a bug in OCaml? Is there a way to force a specific type
for an arg to a function?

Rich.

-- 
Richard Jones, Red Hat Inc. (London) and Merjis Ltd. http://www.merjis.com/
http://www.annexia.org/ Freshmeat projects: http://freshmeat.net/users/rwmj
'There is a joke about American engineers and French engineers. The
American team brings a prototype to the French team. The French team's
response is: "Well, it works fine in practice; but how will it hold up
in theory?"'

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