Re: ANNOUNCE: gtkmm 2.91.7

[Murray Cumming <murrayc murrayc com>]

On Fri, 2010-12-24 at 13:14 +0100, Krzesimir Nowak wrote:
> 2010/12/22 Murray Cumming <murrayc murrayc com>:
> > On Wed, 2010-12-22 at 12:31 +0100, Murray Cumming wrote:
> >> WARNING: TreeViews seems to be mostly empty in this version, but I'm releasing
> >> this unstable version anyway. Maybe someone can discover what the problem is.
> >
> > This is not a problem with plain GTK+, so maybe something in gtkmm is
> > causing it. Maybe some vfunc, for instance.
> >
> > I'm not likely to have much time over the next few weeks, so I'd
> > appreciate any help in debugging this.
> >
> 
> I have some suspicions about newly introduced cell stuff.
> Especially a piece of code in gtkcelllayout.c beginning from line 133:
> 
> if (iface->pack_start)
>   iface->pack_start (cell_layout, cell, expand);
> else
>   {
>     area = iface->get_area (cell_layout);
> 
>     if (area)
>       gtk_cell_layout_pack_start (GTK_CELL_LAYOUT (area), cell, expand);
>   }
> 
> The `if (iface->pack_start)' is true, because gtkmm puts there its own
> function calling a C++ virtual method if possible. But none is called
> when a type is not a derived one (here - Gtk::CellRendererText), so
> it tries to call the original C vfunc. But this vfunc is NULL, so in the
> end `iface->pack_start (cell_layout, cell, expand);' is a NOP. In that
> case `else' part should be executed, but in C++ it isn't. This should
> probably be fixed in C by giving GtkCellRendererText pack_start
> vfunc a body in `else'. What do you think?

CCing Tristan, the author of that code, who might agree.

In general, yes, it is a bad idea for C GObjects to check if a vfunc is
NULL. It should do default behaviour in a default implementation, not in
the case that there is no default implementation. 

-- 
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