[Gtk2-perl-bugs] [Bug 573493] New: suggest call-out for GObject "constructor" func

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  gnome-perl | Glib | Ver: unspecified
           Summary: suggest call-out for GObject "constructor" func
           Product: gnome-perl
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: Normal
         Component: Glib
        AssignedTo: gtk2-perl-bugs@...
        ReportedBy: user42@...
         QAContact: gtk2-perl-bugs@...
     GNOME version: Unspecified
   GNOME milestone: Unspecified


With Perl-Gtk 1.200 and Gtk 2.12.11 the foo.pl below gets an error

GLib-GObject-CRITICAL **: g_object_set_property: assertion `G_IS_OBJECT
(object)' failed at foo.pl line 12.

I believe GtkFileChooserDialog dispatches chooser properties like 'action' to
its child GtkFileChooserWidget, but that widget is only created by the
GtkFileChooserDialog "class->constructor" func and is thus not available in a
subclass INIT_INSTANCE.

It'd be good to have a way to run code in the constructor() stage of a
subclass.  The gobject docs say this is supposed to be rarely needed, but
cooperating with what a superclass like GtkFileChooserDialog does in a
constructor() would be a good use.

If the docs are to be believed constructor stuff normally runs bottom-up, ie.
the first thing you do is call to the superclass constructor.  In theory it
looks like maybe you could mangle the GObjectConstructParam pspec+values going
to the superclass, or something like that.  So maybe an arbitrarily chainable
scheme could be wanted, at least eventually.

The workaround I got to for a perl subclass of GtkFileChooserDialog was to make
my own new(), and set ChooserWidget properties in there. Of course subclassed
new() is outside the GObject mechanism, not reached by non-Perl constructor
code.  For example making such a subclass with the GtkBuilder mechanism doesn't
reach that new() code.


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  gnome-perl | Glib | Ver: unspecified




------- Comment #1 from Kevin Ryde  2009-02-27 23:46 UTC -------
Created an attachment (id=129695)
 --> (http://bugzilla.gnome.org/attachment.cgi?id=129695&action=view)
failing ChooserDialog subclass program


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  gnome-perl | Glib | Ver: unspecified




------- Comment #2 from Torsten Schoenfeld  2009-03-01 12:43 UTC -------
Created an attachment (id=129778)
 --> (http://bugzilla.gnome.org/attachment.cgi?id=129778&action=view)
GObject constructor and constructed discussion

This came up about two years ago in a discussion between Emmanuele, muppet, and
me.  I don't recall every detail now, but I think the conclusion was that it is
better to have a CONSTRUCTED that mimics GObject::constructed.  I attach the
mail discussion in HTML form (converted by mhonarc).

Can you see a way out of this labyrinth?


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  gnome-perl | Glib | Ver: unspecified




------- Comment #3 from Kevin Ryde  2009-03-03 00:26 UTC -------
Me?  Nope, it's a maze of twisty passages.  The construct-only properties was
something I wondered about too, but don't really need.

I see the bit about how a vfunc can find its superclass came up yet again.
That seems like a hydra.  If the C funcs have to implicitly know their
superclass it might be necessary to build a new func for each subclass at
runtime.  Not hard to make some asm bytes, but being thread-safe, portable, and
coping with normally no-exec data segments could be painful.


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