Re: [Caml-list] coercions from superclass to subclass?

[Alessandro Baretta <alex@baretta.com>]

Michael Vanier wrote:
> I understand that there is no mechanism to coerce from a superclass to a
> subclass in ocaml (i.e. the equivalent of C++'s run-time type
> identification or java's instanceof operator).  Are there any plans to add
> such a capability in the future?
> 
> Mike

Jacques Garrigue gave the following explanation a week ago.

 > By the way, here is a simple way to do downcasts, when
 > really needed.
 >
 > # let tbl : (< >, impl) Hashtbl.t = Hashtbl.create 17
 >   let register obj = Hashtbl.add tbl (obj :> < >) obj
 >   let recover obj = Hashtbl.find tbl (obj :> < >) ;;
 > val tbl : (<  >, impl) Hashtbl.t = <abstr>
 > val register : impl -> unit = <fun>
 > val recover : < .. > -> impl = <fun>


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