Re: Function completion for GVariant maybe types?

[Markus Elfring <Markus Elfring web de>]

> > I would like to achieve a mapping of nullable objects to indeterminate
> > checkboxes for example.
>
> A GVariant with 'maybe' type seems far too complicated for this.

Why?

I find that "GVariant" provides a general interface for the handling of nullable
data types.


> I'd use an integer holding a tristate enum, { NO, INDETERMINATE, YES } (or
> possibly a pair of booleans, to match how GtkCheckButton works).

Why do you prefer to use an enumeration instead of the other general application
programming interface?


> If you need variants for some reason, { GVariant of type 'b' with value
> FALSE, NULL, GVariant of type 'b' with value TRUE } is also a perfectly
> good tristate.

I agree in principle. Now you try to reduce my request to a special case while I
am still looking for a more general solution.


> If, for some reason, you absolutely need non-NULL variants with type
> 'mb' ("maybe boolean"), then you already know that your data model is
> that you have variants of that type; so you can just make one of these
> objects whenever you need a new variant, and you're done:

I do not think that I can refer to such preallocated objects if I would like to
reuse a template class like "Gtk::TreeModelColumn".


> There's no need to add functions to GLib for this; and in the time
> you've spent arguing about it, you could have implemented all three of
> those possibilities and possibly more, chosen the one you liked best,
> and got on with whatever high-level problem you were solving.

I have got still a different opinion here which I tried to demonstrate in a
draft for the function "g_variant_new_nothing_from_type".
https://mail.gnome.org/archives/gtk-devel-list/2011-December/msg00018.html
http://article.gmane.org/gmane.comp.gnome.gtk+.devel.general/21768/


> If your data model is "I have a variant, and I don't really know what it
> means" then... you don't really know what it means, and you can't do
> anything particularly useful with it until you find out.

I disagree to your conclusion here. - I would like to copy the data type
information from the contained value into a new "Nothing GVariant" in an
efficient way. I do not really want to know the concrete copied data type if I
would like that this operation will be supported in a generic way so that it can
be reused by other class libraries like "glibmm".


> Model-view-controller programming shouldn't be an excuse for speculative
> generalization. Don't make things more complicated than they need to be;
> software is usually quite complicated enough already.

I see opportunities for further fine-tuning and improvement of the involved APIs.

Regards,
Markus