refptr based tree model

[Balazs Scheidler <bazsi balabit hu>]

Hi,

I'm trying to create a custom tree model. My data structure contains a
tree of reference counted objects. The problem I have is that I'm unable
to put a Glib::RefPtr<MyObject> instance (which represents a node in my
tree) to Gtk::TreeIter.

I was following the code in examples/treemodelcustom/, it simply uses
Gtk::TreeIter->gobj() (e.g. GtkTreeIter structure) to represent an
iterator (e.g. a reference to a tree-node). I guessed the reason to use
gobj() instead of C++ members, is that GtkTreeIter is not a real class
in GTK+, and instances of that structure are defined/passed around in
plain C code.

So if my guess above is true, I also have to put a node reference (e.g.
a value of type Glib::RefPtr<MyObject>) to GtkTreeIter somehow.
GtkTreeIter defines 3 pointers (12 bytes) for this purpose.

My problem:

1) I cannot extend Gtk::TreeIter to define a Glib::RefPtr<MyObject>
member
2) I cannot get a "raw" pointer from Glib::RefPtr<MyObject> which I
could put into GtkTreeIter

The only solution right now that I can see, is to create a "Glue" class,
that holds a reference to my node and store a pointer to this glue class
in GtkTreeIter. Then have some mechanism in place that ensures that Glue
instances get freed. However I don't really like this solution (why
allocate a new object just to store a simple pointer?), and I'd like to
avoid this if possible.

Any other ideas?

-- 
Bazsi