Re: A little tie magic

["A. Pagaltzis" <pagaltzis gmx de>]

* Bjarne Steinsbø <bosteins broadpark no> [2003-12-07 18:37]:
> 1) Is there enough interest in this that the powers that be
> should be requested to include it in the core Gtk2
> distribution?
> 2) Is this the way the interface should work?  Any better
> suggestions?
> 3) Would it be OK to document Gtk2::BindVariable as such, even
> though at least one additional method will be compiled into
> each and every Gtk2 'client' class?

I don't see why this has to be a Gtk2-specific module. Instead of
having all the widgets support ties, you should implement a
change-notifying scalar using the tie mechnism along these lines: 

  package Tie::NotifyScalar;
  require Tie::Scalar;
  our @ISA = qw(Tie::Scalar);
  
  sub TIESCALAR {
    my $pkg = shift;
    my ($updated) = @_;
    bless {
      data => \(my $data),
      callback => $updated,
    }, $pkg;
  }

  sub STORE {
    my $self = shift;
    my ($value) = @_;
    $self->callback($self->{data}, $value);
    $self->{data} = $value;
  }

  sub FETCH {
    my $self = shift;
    # unexpected aliasing effects possible if return is not a true copy
    return my $data = $self->{data};
  }
  
Now you have a scalar that runs a callback whenever it is
updated. In your app you then do something like
  
  tie my $button_label, 'Tie::NotifyScalar', sub { $button->set_label($_[1]) };

Now whenever you change $button_label, the button label will
change as well. No need to add tons of stuff to Gtk2.

Maybe I should add proper sanity checks to this code and a bunch
of tests and up it to CPAN?

-- 
Regards,
Aristotle
 
"If you can't laugh at yourself, you don't take life seriously enough."