Re: How do I retrieve the 'type' of an object

[muppet <scott asofyet org>]

(sorry if this comes through twice -- my MUA is giving me fits)

On Sunday, June 6, 2004, at 06:32 PM, Daniel Kasak wrote:

> I'm looping through a set of objects, and I want to get the type of 
> object, ( eg GtkEntry ) and then decide what to do based on the type.
> How do I do that?
> eg:
>
> >     foreach my $field (@{$self->{fieldlist}}) {
> >                     my $widget = $self->{form}->get_widget($field);
> >                 # Need to figure out what type of object $widget is
> >             }

i'm presuming you are trying to write a generic handler for a bunch of 
widgets in a form.  for example, you have an array of widgets which may 
be entries for strings, or spinbuttons for numbers, or combos for 
enums, etc.

in that case you want to handle the number, string, and enum types 
differently.

what aristotle said, that you don't want to differentiate by types, is 
true; that breaks the ability to use subclasses of things.  in this 
situation, though, polymorphism will require multiple inheritance, 
which can be a bit much work, so effectively "switch"ing on object type 
is a decent idea.  and, of course, you use perl's "ref" operator to 
tell into what class an object is blessed.

*however*, in practice, you don't want to know *exactly* what type your 
object is; you only care if it is descended from the right type.  you 
use "isa" for that:

   foreach my $field (@{$self->{fieldlist}}) {
       my $widget = $self->{form}->get_widget ($field);
       if ($widget->isa ('Gtk2::SpinButton')) {
          # you use spinbuttons for numbers
       } elsif ($widget->isa ('Gtk2::OptionMenu')) {
          # optionmenus are used for the enum stuff
       } elsif ($widget->isa ('Gtk2::Entry')) {
          # it's an entry, so you have a string.
       } else {
          # don't know how to handle it.
       }
   }




--
muppet <scott at asofyet dot org>