Re: [Chicken-users] Passing C pointers into C++ code

[John Lenz]

On 12/19/04 04:15:09, felix winkelmann wrote:
> On Thu, 16 Dec 2004 21:52:52 +0000, Joel Reymont <address@hidden> wrote:
> > Folks,
> >
> > I'm trying to pass a C pointer into a C++ function. This is what I get:
> >
> > (setTarget graphics (slot-ref screen 'swig-this))
> >
> > Error: (class-of) can not compute class of primitive object: #<SWIG-
> > pointer 163c4a0>
> >
> > What does this mean?
> >
>
> TinyCLOS currently doesn't know about swig-pointers. I'll fix
> this. `setTarget' looks like a generic function, so it want's to compute
> the
> class of the argument values to dispatch to the proper method.

Yeah, the guile module is able to extract the SWIG pointer from the wrapped  
proxy class, but I am not sure how to do it for chicken.  Basicly, in the  
function that accepts a SWIG pointer, we need to do something like (this is  
what the guile module does)

if (arg is tinyclos class) {
 arg = (slot-ref arg 'swig-this)
}

if (arg is SWIG pointer) {
 ... whatever
}

The problem is, is there any way to access (slot-ref arg 'swig-this) from C  
code?  The only way I could think of to do it is to use a callback.  That  
is, inside the SWIG generated scheme file do something like

(Foo-registerswighelperfunction (lambda (x) (if (slot-ref x 'swig-this)))  
or better yet
(lambda (x) (if (instance? x) (if (memq? 'swig-this (class-slots (class-of  
x))) (slot-ref x 'swig-this) x) x))

Just for reference, here is my response to the original question on the  
SWIG mailing list.
http://mailman.cs.uchicago.edu/pipermail/swig/2004-December/011208.html