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Date: 2002-07-23 (08:39)
From: Xavier Leroy <xavier.leroy@i...>
Subject: Re: [Caml-list] CamlIDL and function pointers
>   How would one annotate the following C struct for camlidl:
> typedef struct funp {
>    int i;
>    void (*funp_fun) ();
> } funp_t;
>   Is it possible? Looking at the specs I don't see how one can have a
> field that is a pointer to a function. Any ideas, or pointers (no pun
> intended) to examples?

CamlIDL, like the DCE and Microsoft IDL from which it derives, doesn't
support exchanging function pointers between C and Caml.  Your best
bet is to declare funp_t as an abstract type in the IDL file:

        typedef [abstract] struct funp * funp_t;

and export C functions that do what you need to do on this funp_t
type, e.g.

        void invoke(funp_t arg);

where "invoke" is defined directly in C somewhere else:

        void invoke(funp_t arg) { arg->funp_fun(arg->i); }

Of course, you won't be able to, say, construct a funp_t where the
function part is actually a Caml function.  If you need that kind of
callback mechanism, you'll have to write some of the stub code by hand,
using Caml's callback functions.  Alternatively, if you can re-shape
your struct funp till it looks like a COM interface, you could then use
the CamlIDL "interface" declaration and get Caml->C and C->Caml calls.

Hope this helps,

- Xavier Leroy
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