[Gtk2-perl-bugs] [Bug 161012] Feature Request: Gtk2::TreeIters should be able to store data

[<bug...@bu...>]

http://bugzilla.gnome.org/show_bug.cgi?id=161012
gnome-perl | Gtk2 | Ver: unspecified





------- Additional Comments From sc...@as...  2004-12-16 08:12 -------
While GObject is reference-counted and therefore can be better managed for lifetime, passing a 
GObject pointer where a GtkTreeIter pointer is wanted is pretty dangerous.  I would imagine that the 
only reason you got away with it is that since GtkTreeIter is just a plain struct, gtk+ can't do sanity 
checks on it and so doesn't (it contains no type id).  Even though you created a GObject with stamp and 
user_data fields, the compiler will not find them at the safe struct offset, so code compiled to work with 
a real GtkTreeIter will fail mysteriously with a GObject --- it will think that the GObject's type id is the 
stamp, for example.

Furthermore, while gtk+ does no type checks on GtkTreeIters, the bindings expect that they are plain 
structs to be treated as GBoxed types, and will do the exactly wrong thing to a GObject pointer.  Let's 
track a call to gtk_tree_model_get_value() through both C and perl to see what i mean:

C:  you've passed a GObject * to gtk_tree_model_get_value() for the iter.

gtk_tree_model_get_value() checks that iter != NULL.  This is true.
gtk_tree_model_get_value() calls get_value() vfunc from your model's iface.  This actually calls a 
function in your custom model, which expects a GObject, so things mostly work.  If you passed it to a 
built-in model, however, it would eventually cause a segfault when gtk+ tried to use the bogus data.

Perl:  you attempt to pass a Glib::Object reference to Gtk2::TreeModel::get()

Gtk2::TreeModel::get() calls SvGtkTreeIter() to fetch the pointer from the reference in ST(1).
SvGtkTreeIter() is a macro (defined in gperl-autogen.h) that evaluates to gperl_get_boxed_check((sv), 
GTK_TYPE_TREE_ITER)).  GTK_TYPE_TREE_ITER is a boxed type id, and gperl_get_boxed_check() will look 
up the registered boxed wrapper (the default, in this case), which assumes that the SV points to a 
wrapper struct containing the type id, a boolean saying whether the wrapper owns the struct, and a 
pointer to the struct; however, you've actually passed a magical GObject reference.  The wrapper class's 
unwrap vfunc, in this case default_boxed_unwrap() in in Glib/GBoxed.xs, calls sv_derived_from() to 
verify that the reference is blessed into the package associated with GTK_TYPE_TREE_ITER, "Gtk2::
TreeIter".  However, your type is derived from Glib::Object, so this check will fail with the message 
"MyFoo is not of type Gtk2::TreeIter".

That is, you can't even get through the bindings to pass the wrong thing.


So, i don't think using a GObject for the iter will help.

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