Re: GLib/perl and GArray, GType

[Wouter Verhelst <wouter nixsys be>]

On Thu, Dec 11, 2008 at 12:31:09AM -0500, muppet wrote:
> On Dec 9, 2008, at 5:09 PM, Wouter Verhelst wrote:
>
> > I've been using GObject and the GLib perl module to write some
> > object/relational mapper. Mostly for fun (stop looking at me weird!),
> > but it's working out quite well.
>
> Hey, some of us like writing language bindings, so you're in good  
> company for weird.

Heh :-)

> > One thing I'm not very happy about is the way I have to work with
> > GArrays and GTypes in the XS API. Every time my API returns more than
> > one object, it uses GArrays to do this (although I'm thinking of
> > changing that to GLists). As far as I can see in "perldoc  
> > Glib::xsapi",
> > the perl module doesn't do any black magic to make sure that GArrays  
> > (or
> > GLists, or GSLists, or whatever) are automatically converted from and 
> > to
> > perl lists. Is this correct? If so, it's not a huge deal--I can live
> > with having to allocate an array and deallocate after having converted
> > it to a perl list, but it would be nice to not have to do this *every
> > time*. It gets boring :-)
>
> The GArray and GList do not specify the type of what they contain.   
> Therefore, there's no generic way to convert them.  You're always open  
> to somebody deciding to be cute and have the first element be an object, 
> the second be an int cast as a pointer, and the third be a boxed type.  
> You'll crash on the second one, and probably the third one, too.

Right, that makes sense.

> Now, it's fairly easy for you to create a function that knows how to  
> convert an array of whatever, and create a typemap for that.  Then you  
> can use that all over the place in your own code.

Sounds like that could work. Having said that, I've not done much XS
code beyond this project, and since your code has generated all my
typemaps there (thanks, BTW), I wouldn't know where to start. Care to
give me a pointer? ;-)

[...]
> > Secondly, "perldoc Glib" suggests that every time you want to use a
> > GType, the Perl version will be that you use a package name. A
> > particular part of my API has a property that is a GType; it uses
> > g_param_spec_gtype(), and this works from C. Unfortunately, the Glib
> > module doesn't see this; I get errors about "Foo::Bar" not being a  
> > valid
> > integer (despite it having been registered as a GObject package). Is
> > there any way to make this work, other than an ugly hack of adding a
> > perl-specific 'foo_bar_get_type_property' sub in the XS file?
>
> Hey, GParamSpecGType looks damned handy.  It's new in 2.10, and appears 
> to be unsupported in trunk of perl-Glib.

I see; that explains it.

> It looks like it uses GValues that hold G_TYPE_GTYPE, so we should be
> able to set up marshaling logic in GValue.xs that calls
> gperl_package_from_type() and  gperl_type_from_package() to do the
> magical conversions.
>
> I had knocked together a patch that implements this, but working the  
> kinks out of value coercion in the unit test expanded to fill all my  
> available time for the evening, which was about half an hour.  :-(   I'll 
> try to get you a working patch later this week.

That'd be great, thanks; and if you don't make it this week, there's no
rush -- I know what's going on, and this is (mostly) a hobby project
anyway.

-- 
Wouter Verhelst
NixSys BVBA
Louizastraat 14, 2800 Mechelen
T: +32 15 27 69 50 / F: +32 15 27 69 51 / M: +32 486 836 198