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* (fwd) Re: Problem with guile-gobject-0.5.1
@ 2003-08-07  8:07 Andy Wingo
  0 siblings, 0 replies; only message in thread
From: Andy Wingo @ 2003-08-07  8:07 UTC (permalink / raw)
  To: guile-gtk, Patrick Bernaud

I'm forwarding this, as I think me email was being flaky before and
somehow exim lost this one. Argh!

----- Forwarded message from Andy Wingo <> -----

> From: Andy Wingo <>
> Subject: Re: Problem with guile-gobject-0.5.1
> To:
> Cc: Patrick Bernaud <>
> Mail-Followup-To:,
> 	Patrick Bernaud <>
> Hi Patrick,
> I'm replying to the list, because that's where this sort of question
> should go. My apologies for being so late. I live in rural Namibia and
> my internet is slow as sap, and I only connect every week or so.
> On Mon, 30 Jun 2003, Patrick Bernaud wrote:
> > I am evaluating the use of your project to wrap around (and extend)
> > libraries based on Glib/Gobject/Gtk.
> Great!
> > However I am having a problem: I do not understand how to manipulate
> > gboxed types from guile.
> > 
> > Here is an example. Let's consider the following definition of the
> > type Point in the .def file:
> > 
> > (define-boxed Point
> >   (in-module "MyModule")
> >   (c-name "MyPoint")
> >   (gtype-id "MY_TYPE_POINT")
> >   (fields
> >    '("gint" "x")
> >    '("gint" "y")
> >    )
> >   )
> Well yes. Interpreted languages need custom wrappers for boxed types. I
> suppose the support could somehow use the field names there to access
> the structure members... but boxed types are usually a sign that
> something is not convenient to represent as an object, on the C side of
> things.
> If it's a refcounting or a speed issue, then there should be C functions
> provided to operate on the object.
> If it's represented as a boxed type for convenience and memory usage,
> then there's usually a better way to wrap it in scheme. In the case of a
> point, I would just have a pair, with the car as x and the cdr as y.
> If the type is more complicated than that, representing it as an object
> is usually the right way to go.
> If you're defining a type in a custom project, why not a GObject?
> Indeed, the only thing the defs parser cares about is
> > (define-boxed Point
> >   (c-name "MyPoint")
> >   (gtype-id "MY_TYPE_POINT")
> >   )
> The other information is superfluous. It's impossible to do at runtime,
> although automagic generation of my_module_my_point_set_x () and its
> get() counterpart is possible I suppose. It's just a nasty solution.
> Gah. I twitch when I think about it. Perhaps someone has thoughts on
> this?
> > Firstly I do not know how to create such a point from guile. I added a
> > constructor to the library and the following to the .def:
> > 
> > (define-function new_point
> >   (c-name "new_point")
> >   (is-constructor-of "MyPoint")
> >   (return-type "MyPoint*")
> >   )
> > 
> > where my_point has the following prototype :
> > 
> > MyPoint *new_point();
> > 
> > and it works. But is it the right way to create a boxed type? Any
> > other way?
> Yes, that's the right way, if you want it to be an opaque type, only
> accessible by C functions. Otherwise you'll have to wrap it specially,
> either on the g-wrap level or by providing C functions to wrap it. There
> are examples of both in gst-guile, although more documentation on this
> would be nice. I'd like to write a nice article about the binding
> generator, but I don't have the time right now.
> > Sorry if it is obvious, but I did not find the solution in the files
> > of the package. There is also few projects around that are using
> > guile-gobject, so it is hard to have an example. I know of gstreamer,
> > is there any other of interest?
> I guess it's not really obvious, I spend so much time staring at this
> code I forget what I was and wasn't born with ;) I don't know of any
> other projects that are using the bindings. My soundscrape project
> ( uses the gstreamer bindings a lot
> and the wrapper generator a little bit. Things have been changing quite
> a bit on the gst-guile side recently, but they seem to be settling down
> But no, I don't know of any other ones. Anyone out there want to speak
> up? It's only been since a couple of months ago that the wrapper
> generator even exists, so it's not so surprising.
> > Thank your for your time.
> And thank you for your interest, and apologies again for the delay.
> Andy Wingo.

----- End forwarded message -----

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2003-08-07  8:07 (fwd) Re: Problem with guile-gobject-0.5.1 Andy Wingo

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