I don't get how the topic applies to my Perl program. It is basically one big switch.

$foo = indirect user input;

given ($foo) {
    when (A) {
        a;
    }
    when (B) {
        b;
    }
    when (C) {
        b;
        one additional statement;
    }
    when (D) {
        d;
    }
    default {
        similar_to_a;
    }
}
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Following the advice in the video, I converted the different blocks into subroutines with the same name under differently named subclasses.

However, I have no idea what to write in the base class. There are no examples. I expected something on the design patterns wiki under the lemma ConditionalElimination at slowass.net, but it's down.

First, I need an abstract method. Is it just sub foo {}; or sub foo; or what? Or should I leave the declaration away altogether?

Second, but most important, now that the switch is gone, how do I go about from user input $foo to a certain subclass foo method? Drawing a blank here.

Third, sharing code between B and C is more difficult. Formerly, when everything was in one package, I just had a sub for the common code. How do I handle that now that they are in different classes?

I'm not convinced that once I solve the problems, the conversion is going to be a big win, but I want to learn it anyway for the future. Please answer accordingly.