Re: [GI] Generic array type

[Daniel Espinosa <esodan gmail com>]

Have you explored Gee?

It uses Vala's generics and provides API to iterate on collections. It has
lot of implementations for generic collections you can use with virtually
any GTYPE object.

Just consider:

a) Generics returning values are not supported in Python and GJS but you
just need to add convenient methods returning actual GType values (GBoxed
ones for example).

b) You can implement Gee interfaces for yourself but requires to create
GObject classes implementing 2 or 3 interfaces. The result helps to avoid
using any Gee container overhead.

c) Vala generics are hard to use from C. You can add wrapper methods to
make your users lives easy (applies to Python and GJS too).

d ) You can use Vala to create your wrappers but add Vala compiler
dependency, and yes just use -C to convert Vala code to C and add resulting
file to your existing list of C code files.
El feb 13, 2015 12:57 PM, "Colomban Wendling" <lists ban herbesfolles org>
escribió:

> Hi,
>
> I'm trying to generate a gobject-introspection binding for a library,
> and am facing some problems I couldn't find the answer to.
>
> First, no, the library isn't really GObjec-based.  However that was not
> the problem, I added appropriate boxed GTypes, and the GIR mostly works
> [1][2].  So, my GIR works mostly as expected from Vala [3], Python and
> GJS.  Great.
>
> However, here comes the tricky problem:  my library has a custom generic
> value type, which supports integers, reals, strings, and arrays.  So, I
> wanted to add wrapping API that take GValues to integrate seamlessly
> with the languages:
>
> ..._push_gvalue(..., GValue *value, ...);
>
> so that the higher level language using the GIR could pass natural types:
>
> ...push(..., 42);
> ...push(..., "hello");
> ...push(..., [1, 2, "hello", [2, 3, 4]]);
>
> It works just fine with integers, reals and strings.  But it doesn't do
> anything good with arrays.
> The problem is, I guess, because GI doesn't have a canonical generic
> array type [4], so language bindings don't know what they should do when
> trying to pass an array as a GValue.
>
> Python passes in a boxed PyObject (what am I supposed to do with that?),
> GJS basically errors out complaining it can't convert the array, and
> Vala doesn't compile code passing in a native array (`int[]` for
> example, nor even `GValue?[]`).
>
> With Vala I can make it work by explicitly giving a `Array<Value?>`,
> which properly gets boxed, and that I can read (of course, it's plain C
> after all), but I can't even find these APIs in Python or GJS.
>
> Of course, I could add separated API for arrays like this:
>
> ..._push_gvalue_array(..., GValue **values, gsize n_values, ...);
>
> It works, but of course only for a single-level array (fails the same
> with an array containing array members) -- and having separate API for
> the array case is also not very nice.
>
> I also gave GVariant a quick shot, but while it works quite well with
> Vala (well, similarly to GValue, with the addition it knows about
> arrays), it doesn't seem to have any kind of magic integration for
> creating variants with Python or GJS [5] -- and then becomes extremely
> verbose.
> Also, I'm not quite sure GVariant is meant to be used that way, so maybe
> it's abusing the API?
>
>
> Anyway, my question is:  is there a way to pass generic arrays
> implicitly as GValue (e.g. a GArray of GValue*, but I'm open to anything
> usable from C), or is this a lost cause?
>
> And if my only way is to manually build arrays, does Python and GJS have
> a way of building a GArray, or some other similar GLib array type?
> There is no constructor for GLib.Array in GJS apparently, and I didn't
> find any in Python either.
>
>
> BTW, I similarly need to be able to return an array and this array be
> usable by the calling language.  Returning a GArray boxed in a GValue
> "works", but that array is not really usable (not interface to access it
> in Python, and GJS tells me without surprise that it is "Unable to
> introspect element-type of container in GValue").  GVariant seems a
> little more usable there.
>
>
> Thanks for reading through :)
>
> Regards,
> Colomban
>
>
> Notes:
>
> [1] though, while it works with GJS and Python, apparently Seed doesn't
> allow boxed types of unknown size and asserts out when calling the
> constructor.
>
> [2] but apparently boxed type constructors can't have arguments, which
> is somewhat problematic -- but that's not important for me, at least not
> now.
>
> [3] Vala is a bit annoying because of
> https://bugzilla.gnome.org/show_bug.cgi?id=670167, but I get it and it
> can be worked around.
>
> [4] there is GValueArray, but it's now deprecated.
>
> [5] but Python seems to have some support for reading them, as they are
> iterable, printable, and (to some extent) usable as a value
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