Re: Gtk2::Ex::Simple::(List|Tree)

[muppet <scott asofyet org>]

On Oct 28, 2004, at 4:48 AM, Vincent LADEUIL wrote:

> The missing bits, again :o) I search for that, but failed :-/
[snip]
> ...and the  missing link !  Ok, things are  clear now (did  I say
> that before ? :o)
[snip]
> Enlightment !

do you have suggestions for where or how this should be explained in 
the documentation?  i think i am too familiar with it to understand 
fully how to explain it to the uninitiated -- at least, our current 
docs reflect that.


>    sub new {
>        my ($class, $something) = @_;
>        # we can't do $class->new(), because we're overriding that.
>
> Don't   get    that   >-/   Did    you   mean   you    can't   do
> $class->new($something) or just that you had added a parameter ?

perl method lookup is done purely at runtime, *after* the compile 
phase, and is done purely on name, not parameters (as in C++).  so in 
Foo::bar(), a call to Foo::bar() will resolve to the exact same 
function -- you'll call yourself indefinitely.  Foo::SUPER::bar() will 
skip Foo::bar() while looking through @ISA for bar(), but i explained 
next why i decided not to do that.


>        # we could do $class->SUPER::new() if we knew its call 
> signature.
>        # instead, i'll go straight to Glib::Object::new, because i know
>        # it will call each INIT_INSTANCE in the ancestry to initialize
>        # the object properly.
>
> I'm sure I had already read that comment somewhere, I searched
> for it whereever I can think of, Gtk2 doc, tutorial, examples,
> can't put my finger on it ! Thanks so much :o)

i would've sworn that was mentioned in either 
http://gtk2-perl.sourceforge.net/doc/pod/Glib/Object/Subclass.html or 
http://gtk2-perl.sourceforge.net/doc/subclassing_widgets_in_perl.html , 
but apparently i was wrong; it seems to be assumed or inferred.  it is 
explained in the gtk+ documentation, but i doubt many perl programmers 
will read about the guts of doing OO in C.  ;-)


> But  it  means,  that  it  works  for  only  one  level  of  perl 
> inheritance isn't it ?

GObject only allows single inheritance; that means one parent at a 
time, e.g., only one GObject in @ISA; GObject uses Interfaces in place 
of multiple inheritance, but the perl bindings just use perl's @ISA.

you can, however, derive a new perl gobject from a perl-derived 
gobject; the Glib test suite verifies this.  everything is based on 
package names, and the fact that INIT_INSTANCE and friend are called 
from C when g_object_new() walks the ancestry.

wow, that's not very clear.  sorry.


--
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With treatment, it will last about a week.
  -- conventional wisdom