Re: [sigc] conditions in libsigc

[Murray Cumming <murrayc murrayc com>]

On Fri, 2006-07-07 at 22:42 +0300, Paul Pogonyshev wrote:
> Currently, you have to 1) set sensitivity (some state) to a computed value;
> 2) track when that computed value changes its state, by connecting to the
> appropriate callbacks; if the rules change, you have to not forget to keep
> the computation and state tracking in sync; and 3) set the initial state
> (sometimes).  Note that the initial state should also be in sync with
> points 1) and 2).
> 
> I propose to do all the steps at once, using `condition's.  This roughly
> corresponds to step 1), while all the rest is done automatically.
> 
> Using conditions (doesn't work currently, of course; how it should look
> like):
> 
>     button->set_sensitive (entry->get_not_empty_condition () & check_button->get_active_condition ());

This is an interesting idea, but I have no idea how you might implement
it.

> Traditional method:
> 
>     entry->signal_changed ().connect (sigc::mem_fun (*this, &Windows::update_sensitivity));
>     check_button->signal_toggled ().connect (sigc::mem_fun (*this, &Windows::update_sensitivity));
> 
>     // Set initial state.
>     update_sensitivity ();  
> 
>     ...
> 
>     void
>     update_sensitivity ()
>     {
>       button->set_sensitive (entry->get_text_length () > 0 && check_button->get_active ());
>     }

Yes, I do this quite often.

> > Note also that you can already get notification of property changes from
> > gtkmm objects, like so:
> > widget.property_something().signal_changed().connect( ... )
> 
> Yes.  I propose to simplify it (writing less code) and make less error-
> prone (all is done only once and in one place.)  This is at a small
> cost to efficiency, which is not important in GUI.
> 
> Paul

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com
www.openismus.com