Mastering Perl/Tk

A Mega-Widget Quick-Start

When first trying to decide if you need to write your own mega-widget, you need to know what you want it to do. What features should it have? Which features are absolutely necessary, and which are extras? After creating this list, prioritize the items according to necessity. At this point, you should have a general idea of what types of widgets your mega-widget requires. The next step is to take a look around at the various resources available (CPAN,^[1] newsgroups, and this book) to see if there is already a widget out there. There is no sense in reinventing the wheel if a widget already exists. You might find one that is close enough to do what you want. If you find what you want, congratulations, you no longer need to keep reading this chapter. Still curious, or didn’t find what you needed? Keep reading!

You won’t learn object-oriented programming here; at least, we don’t intend to try to teach it, as there are entire books devoted to the subject.^[2] The actual techniques we use are pretty straightforward and are fully described in the standard Perl documentation. For instance, this code should make sense to you:

package Frog;

sub new {
    my($class, %args) = @_;
    bless \%args, $class;
}

sub get {
    my($self, $attr) = @_;
    $self->{$attr};
}

package main;

my $frog = Frog->new(qw/-color blue -poisonous 1/);
print "$frog: color = ", $frog->get(-color), "\n";

Frog=HASH(0x80ccf7c): color = blue

If this code is unclear, or if terms like base class, subclass, superclass, ...