Re: New to GObject, few questions

[David Nečas (Yeti) <yeti physics muni cz>]

On Fri, Jul 21, 2006 at 10:22:19PM +0200, Tomasz Jankowski wrote:
> I read few times "Gobject tutorial" provided with GLib's documentation but I
> don't understood it enouhg good, maybe because I don't like (and know)
> object languages, I know only C++ basics. So these are my questions:
>
> I. What the Interfaces are? I don't understood their predestination? I
> understood them as other type of Methods, but I'm know, that Interfaces
> aren't Methods, can someone explain me it?

[quote from Sun]
   An interface is a contract in the form of a collection of
   method and constant declarations.  When a class implements
   an interface, it promises to implement all of the methods
   declared in that interface.
[/quote]

This sums it up nicely, except in GObject there are other
things that can be part of an interface, namely signals.
But the principle is the same, an interface is a collection
of APIs a class can claim it provides.

For example, GtkTreeModel is an interface.  So if you write
a new tree model it claims `I am a tree model' and it does
not have to derive from a specific parent class for that
(OK, interface in fact can impose parent class restrictions,
but that's a technical detail).

C++ has no direct analogue because it has multiple
inheritance so it doesn't need it.

> II. For example, object "XXX" inherits from object "ZZZ"

Objects do not inherit, classes do.

> and I defined
> *_finalize () functions for object ZZZ, but I didn't define any *finalize
> functions for object XXX. What will happen if I'll try to destroy XXX
> object? Will ZZZ's *_finalize functions will be used?

Yes, it will.  Moreover, if the class of XXX *does* define
a finalize method, it has to explicitly call the parent's
class finalize:

  G_OBJECT_CLASS(parent_class)->finalize(object);

(see Gtk+ source code for examples).

> III. What 'GTypeInstance' is?

GTypeInstance is a low-level construct in the type system,
it is `an instance of something that has a GType'.  You
should never need it.

Yeti


--
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