Re: [Caml-list] List of structurally typed objects

[Mikhail Mandrykin <mandrykin@ispras.ru>]

On среда, 22 февраля 2017 г. 13:08:23 MSK Ivan Gotovchits wrote:
> It is possible to generalize this approach using private row types.

If at least a limited support for dynamic object typing is needed, it's also 
possible to construct a heterogeneous container of objects using several 
advanced features like first-class modules and GADT, but even in this case the 
exact type of the object should match precisely when extracted from the list 
or at least a finite (and small) number of possibilities for that type should 
be known. It's, however, still possible to upcast the object to some supertype 
upon addition and later extract and use it as the object of that supertype. An 
example: https://github.com/schrodibear/ocaml_tricks/blob/master/object_hlist/
obj_list.ml

Mikhail

> 
> list_fns.mli:
> 
> module Registry(Obj : sig
>     type t = private < .. >
>   end) : sig
>   val register_obj : string -> Obj.t -> unit
>   val get_obj : string -> Obj.t
> end
> 
> 
> list_fns.ml:
> 
> module Registry(Obj : sig
>     type t = private < .. >
>   end) = struct
> 
>   let objs = ref []
>   let register_obj name obj = objs := (name, obj) :: !objs
>   let get_obj name = List.assoc name !objs
> end
> 
> 
> test.ml:
> 
> class foo = object
>   method hello = "hello from foo"
>   method goodbye () = print_endline "goodbye"
> end
> 
> class bar = object
>   method hello = "hello from bar"
> end
> 
> module Bars = List_fns.Registry(struct type t = bar end)
> 
> let () =
>   let o1 = new foo in
>   let o2 = new bar in
>   Bars.register_obj "o1" (o1 :> bar);
>   Bars.register_obj "o2" (o2 );
>   print_endline ("calling o1: " ^ (Bars.get_obj "o1")#hello);
>   print_endline ("calling o2: " ^ (Bars.get_obj "o2")#hello)
> 
> 
> 
> 
> The List_fns.Registry functor will create a monomorphic registry for the
> specified base type.
> 
> 
> Probably, this may help you :)
> 
> Best wishes,
> Ivan Gotovchits
> 
> On Wed, Feb 22, 2017 at 12:38 PM, Richard W.M. Jones <rich@annexia.org>
> 
> wrote:
> > On Wed, Feb 22, 2017 at 06:28:51PM +0100, Damien Guichard wrote:
> > > Hi Richard.
> > > 
> > > Is this the code you want ?
> > > 
> > > type 'a obj_list = 'a list
> > > constraint 'a = < hello : string; .. > as 'a
> > 
> > Perhaps.  Is it possible to write the list_fns.mli interface
> > using this?
> > 
> > Rich.
> > 
> > 
> > --
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-- 
Mikhail Mandrykin
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: mandrykin@ispras.ru