On Mon, 2007-05-14 at 12:12 -0700, Ana wrote:
> On Sat, May 12, 2007 at 02:42:50PM +0800, Kuang-Chun Cheng wrote:
> > On 5/12/07, Jean Br*fort <[1]jean.brefort@xxxxxxxxxxxxxx> wrote:
> ....
> >
> > A GObject class can inherit from only one parent (which might be
> > virtual), but you can add as many Interfaces as you like. It is somewhat
> > similar to multiple inheritance in C++ (more like the D language
> > actually).
> >
> > Hi Jean,
> >
> > That's new to me ... I did not catch up this from GObject Ref. Manual ...
> > Thanks.
> >
> > KC
>
> It's also important to note that GTK+ Interfaces cannot directly
> implement any functionality, unlike C++ classes. They only specify the
> set of (rigid) "prototypes" that *must* be fully implemented by the
> implementing class.
this is not entirely true. since a GTypeInterface is really just a
vtable of function pointers (plus the ability to have a set of
properties that can be overridden and all the stuff that comes from
being a type known to the GType system), it's not necessary for classes
implementing the interface to implement each and every function - as
long as the calls to the interface functions use a check like this one:
if (MY_INTERFACE_GET_IFACE (instance)->some_method)
MY_INTERFACE_GET_IFACE (instance)->some_method (instance, foo);
else
{
warn_abort_or_do_nothing_at_all ();
}
which allows you to have mandatory and optional methods.
there's also the possibility to actually have an implementation inside a
GTypeInterface itself, unlike in Java:
if (MY_INTERFACE_GET_IFACE (instance)->another_method)
return MY_INTERFACE_GET_IFACE (instance)->another_method (instance);
else
{
gboolean bar;
gint foo;
g_object_get (instance, "bar", &bar, NULL);
foo = foobarize (bar);
}
this makes GTypeInterface more like a mixin or a role, in OOP.
ciao,
Emmanuele.
--
Emmanuele Bassi, E: ebassi@xxxxxxxxx
W: http://www.emmanuelebassi.net
B: http://log.emmanuelebassi.net
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