Re: GTKRadioButton groups breakage/weirdness

[Owen Taylor <otaylor redhat com>]

Tim Janik <timj gtk org> writes:

> On Sat, 27 Oct 2001, Joel Becker wrote:
> 
> > GTKers,
> > 	So, the following code does not work:
> > 
> > GtkWidget *a, *b, *c, *d;
> > GSList *group = NULL;
> > a = gtk_radio_button_new_with_label(NULL, "a");
> > group = gtk_radio_button_group(GTK_RADIO_BUTTON(a));
> > b = gtk_radio_button_new_with_label(group, "b");
> > c = gtk_radio_button_new_with_label(group, "c");
> > d = gtk_radio_button_new_with_label(group, "d");
> > 
> > 	Because of the gyrations in gtk_radio_button_set_group, these
> > buttons end up in different groups.  The following code does work
> > though:
> > 
> > GtkWidget *a, *b, *c, *d;
> > GSList *group = NULL;
> > a = gtk_radio_button_new_with_label(NULL, "a");
> > group = gtk_radio_button_group(GTK_RADIO_BUTTON(a));
> > b = gtk_radio_button_new_with_label(group, "b");
> > group = gtk_radio_button_group(GTK_RADIO_BUTTON(b));
> > c = gtk_radio_button_new_with_label(group, "c");
> > group = gtk_radio_button_group(GTK_RADIO_BUTTON(c));
> > d = gtk_radio_button_new_with_label(group, "d");
> > 
> > 	It appears you have to consider your group pointer invalid after
> > every addition, because of the way the list is recalculated.  This is
> > non-obvious, and I'd consider broken.  However, simply documenting this
> > limitation would suffice.  But you have to peruse the source quite
> > heavily to see where this happens.
> 
> jup, this is actually bad API.

Well, yes, that's been known for a long time, which is why
gtk_radio_button_new_from_widget() was added.

> i guess i'd accept a patch that changed radio button groups from GSList
> into GList (and walked group->prev in gtk_radio_button_new_with_label), as
> 1) walking a GList* cast into a GSList* and just accessing ->data will work
>    fine

I really think this is too major a change to make at this point, even
if it would have been desirable a few months ago. A spot check in LXR
reveals thousands of uses of gtk_radio_button_group(), virtually all of
which involve assignment to a variable.

If we were going to change it, I'd make GtkRadioButtonGroup an
opaque data type, or even a GObject, so you could have things
like "gtk_radio_button_group_get_active_widget(). 

But we really have to cut off major and even minor changes at this
point.

Regards,
                                        Owen