Raku version of classic observer pattern example but without a fixed interface.

observer-classic.raku

#!/usr/bin/env raku

role ObserverSignal {
}

multi sub trait_mod:<is> ( Method $m, :$observer-signal! ) {
    $m does ObserverSignal;
}

role Observable {
    has @.observers;

    method signal() {
        for @.observers -> $observer {
            for $observer.^methods.grep(ObserverSignal).grep(*.cando(\($observer, self))) -> $method {
                $observer.$method(self);
            }
        }

    }
}

class Subject is Observable {
}

class Observer {
    method any-old-name(Subject $) is observer-signal {
        say "got Subject signal";
    }

}

my $subject = Subject.new;
$subject.observers.push: Observer.new;

$subject.signal;
# vim: ft=raku