Re: gtk_widget_get_allocation

["Brian J. Tarricone" <bjt23 cornell edu>]

Cody Russell wrote:
> On Thu, 2008-09-25 at 02:02 +0200, Christian Dywan wrote:
> > >      * gtk_widget_get_allocation
> > >        Removed in 2.14.1
> > The prototype of this function was not agreed upon among the core
> > developers. So the decision was deferred to the next Gtk version.
> > It had to be removed before final API freeze, otherwise it could not
> > have been changed anymore.
>
> This is rather old, but it never came up again after this so I'd like to
> see what thoughts are about how to implement this in C.  It was in 2.13
> but removed before 2.14 because of disagreement, but I can't find any
> public record of the disagreement in gtk-devel-list.  Can anyone comment
> on what was not liked, or how a better implementation could be made?
>
> For reference, this is the previous implementation:
>
> GtkAllocation
> gtk_widget_get_allocation (GtkWidget *widget)
> {
>   static GtkAllocation allocation = { 0 };
>   g_return_val_if_fail (GTK_IS_WIDGET (widget), allocation);
>
>   return widget->allocation;
> }

I assume the issue was with returning a non-primitive type by-value and 
not as a pointer.  For modern compilers this isn't a big deal, I don't 
think (but might be inefficient on some arches), but I imagine people 
want to compile gtk on all sorts of systems.  An implementation like 
this avoids that problem, though perhaps isn't as nice to use[1]:

void
gtk_widget_get_allocation (GtkWidget     *widget,
                           GtkAllocation *allocation)
{
    g_return_if_fail (GTK_IS_WIDGET (widget) && allocation);

    memcpy (allocation, &widget->allocation, sizeof(*allocation));
}

(Could also have it return gboolean, but I tend to think it's 
unnecessary to have a success/fail return value when the only reason it 
would fail is if the programmer is using the function incorrectly.)

This seems to be a similar pattern to how other things like this are 
done in gtk...

	-brian

[1] I guess part of the motivation for the original (rejected) 
implementation is so that you can do things like this:

gint width = gtk_widget_get_allocation (widget).width;

Oh well.