Re: Questions about tailoring libdmapsharing API to benefit GObject introspection

[Emmanuele Bassi <ebassi gmail com>]

Hi;

On 12 November 2017 at 23:06, W. Michael Petullo <mike flyn org> wrote:
> > > I am the maintainer of libdmapsharing, a GObject-based library. I am
> > > just now getting around to adjusting the library's API to better suit
> > > GObject introspection. I am not sure how to process on two things
> > > having
> > > to do with object properties.
> > >
> > > One of my interfaces, the DAAPRecord, has among its properties two
> > > items: hash, a GLib2 ByteArray/g_param_spec_pointer and mediakind, a
> > > g_param_spec_enum. I am trying to implement an object of this
> > > interface in
> > > Python, but I am not sure how to proceed with either of these
> > > properties.
> > > (As I mentioned, I am willing to modify the libdmapsharing interface
> > > to
> > > facilitate this if necessary.)
> > >
> > > I am not sure how to best handle hash. Should I create a box type? It
> > > seems like the should be a straightforward approach to handle a
> > > ByteArray.
>
> > Can you provide a link to the code in question, and a copy of the
> > relevant bit of the generated GIR file?
> >
> > My first guess would be that you are right, and it should be a boxed
> > type. See the GTlsCertificate:certificate property for an example.
> >
> > https://git.gnome.org/browse/glib/tree/gio/gtlscertificate.c#n106
>
> > > For mediakind, I get a warning if I try this:
> > >
> > >      class PyDAAPRecord((GObject.GObject, DAAP.Record, DMAP.Record):
> > >             # ...
> > >          mediakind = GObject.property(type=GObject.TYPE_INT, default=0)
>
> > That looks like more of a Python thing, which I can’t help with, sorry.
>
> The code is available with:
>
>         git clone git://git.gnome.org/libdmapsharing

>         <property name="hash" writable="1" transfer-ownership="none">
>                 <type name="gpointer" c:type="gpointer"/>
>         </property>

This is your problem:

https://git.gnome.org/browse/libdmapsharing/tree/libdmapsharing/dpap-record.c#n38

Use g_param_spec_boxed() with G_TYPE_HASH_TABLE.

You'll also need to annotate the property[0] with a gtk-doc stanza and
make the type of keys and values explicit:

https://wiki.gnome.org/Projects/GObjectIntrospection/Annotations#GObject-Introspection_annotations

Look for `element-type` in the context of hash tables.

"Pointers" do not make any sense for language bindings, because
there's no way for them to marshal a pointer to language native data
types.

Ciao,
 Emmanuele.

[0] Actually, for good code hygiene, you should document all your
properties. Relying on GParamSpec fields is just not good enough.

-- 
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[@] ebassi [@gmail.com]