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From: Goswin von Brederlow <goswin-v-b@web.de>
To: Joel Reymont <joelr1@gmail.com>
Cc: caml-list@inria.fr
References: <CAOQwdX1f_RvxeV=NZPaN9-XwSNw3bg_nWzhFMf6Qga0L5Btt9Q@mail.gmail.com>
Date: Thu, 03 May 2012 15:35:49 +0200
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	(Joel Reymont's message of "Thu, 3 May 2012 13:22:49 +0100")
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Subject: Re: [Caml-list] using modules to wrap c++ classes

Joel Reymont <joelr1@gmail.com> writes:

> Suppose I have a C++ class with a bunch of methods that act as callbacks.
>
> My callbacks will be hit if I derive the class and implement the
> methods I'm interested in.
>
> Now, I would like to wrap this class from OCaml.
>
> This is straightforward from using OCaml classes (section 18.3.5 of
> the manual) but is there a way to implement this using modules?
>
> I don't think this is possible but would like to confirm.
>
>     Thanks, Joel

>From the top of my head:

module M = struct
  type t
  external foo : t -> unit = "caml_mine_M_foo"
end


class M {
  void foo(void) { }
};

value caml_mine_M_foo(value ml_m) {
  CAMLparam1(ml_m);
  M *m = (M*)ml_m;
  m->foo();
  CAMLreturn Val_unit;
}

Wouldn't that do?

It gets harder with inheritance, when you have modules A, B, C for the
different classes and want to be able to pass a C.t to a function
expecting a B.t. You will need to declare a C.as_b function and such.

MfG
        Goswin