Re: enum/flag package registration? (was Re: Missing pango constants)

["Ross McFarland" <rwmcfa1 neces com>]

i just got to looking at fixing the scalar problems in Gtk2::SimpleList, it's
really cool and will be in cvs soon. anyway, i came up with a solution based
on some stuff i found in stock_browser. it uses insert_column_with_data_func,
a more complex and flexible version of this, which might work for your case:

$treeview->insert_column_with_data_func (-1,
                'Column Name',
                Gtk2::CellRendererText->new,
                sub {
                    my ($tree_column, $cell, $model, $iter, $i) = @_;
                    $cell->set (style => $model->get ($iter, $column_num));
                },
                , $column_num);

the stuff in SimpleList sets text rather than style and allows you to define
arbitrary new column types so long as you provide a sub that will convert
whatever your $scalar points to whatever text representation you want. this is
a big, and bad, for example, but you could have the scalar contain a
hostname/ip and the sub could ping that returning the round trip time. now
this wouldn't nec be a good way of doing such a thing, but it illistraits how
flexible it is.

ok, sorry got off track on how cool Gtk2::SimpleList is getting, the above
code might work, if not maybe there's something similar that will and this
will get you on the right track. that's assuming that i understand what you're
trying to do.

-rm

muppet said:
> requests for those reading along:  while i ponder under-the-hood fixes, can
> anybody suggest a perl-only workaround?  are there any other situations where
> this sort of problem crops up?
>
>
> Torsten Schoenfeld said:
> > I see. Forget about the patch then and please consider this bug report
> > instead: The above magic somehow doesn't apply to PangoStyle values.
> >
> > When used in a TreeView whose "style" attribute is bound to a
> > Glib::String column and you populate this column with "normal" or
> > "italic", a warning is issued:
> >
> >   (odot:23383): GLib-GObject-WARNING **: unable to set property `style'
> >   of type `PangoStyle' from value of type `gchararray'
>
> well, this is a whole different ball of wax.  it's not that the magic doesn't
> apply to the PangoStyle values --- you are tricking the type machinery!
>
> you see, the string values used to represent enums and flags aren't *really*
> strings; under the hood, they get translated to and from integers via a lookup
> that depends on the GType of the enum or flag type in question.  this warning
> actually comes from deep within the C libs when the objects try to
> communicate; the cell renderer is looking for a GValue with a PANGO_TYPE_STYLE
> enum value in it, but gets a GValue with a G_TYPE_STRING (or G_TYPE_CHARARRAY)
> instead.
>
> in essence, your column type is wrong, and should be Gtk2::Pango::Style type
> instead of Glib::String type --- then the actual enumeration *value* (the
> integer) will be stored in the tree model column instead of a string, with the
> type identifier for validation, and everything should work out.
>
> but that won't work, unfortunately.  when i set up the bindings i didn't
> imagine that this would be a potential use for the enumerated types, so they
> don't get registered into package names.  this shortcut saves startup time and
> memory footprint; there are 143 of these types (out of 334 total) defined in
> Gtk2 alone!  (see the file named "maps")
>
> /me wracks brain trying to figure out how to solve this specific problem
> without incurring a performance hit on the general case
>
> are there any pure-perl workarounds that would avoid the problem?  what's some
> more context on what you're doing --- is it the first way you'd think of doing
> something, or is it sneaky wizzardry[1]?  (i ask because the obvious way needs
> support, but wizardry might be able to suffer at the expense of performance.)
>
> and, most importantly, can anybody think of other cases in which you can't get
> by without (or things are incredibly simplified by) having perl package names
> (which are the perl substitute for GLib GTypes) for GEnum and GFlags types?
>
>
> > Sorry for the noise,
>
> not noise -- discussion is good.  as you see, you uncovered something nasty.
>
>
> [1] you know, like rincewind, with "wizzard" in silver letters on his pointy
> hat. ;-)
>
> --
> muppet <scott at asofyet dot org>
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