Memento

#!/usr/bin/perl6

class Originator {
        has Str $!State;

        method set(Str $State) {
                say "Originator: Setting state to " ~ $State;
                $!State = $State;
        }
        method saveToMemento() returns ::Memento {
                say "Originator: Saving to Memento.";
                return ::Memento.new(:State($!State));
        }
        method restoreFromMemento(::Memento $memento) {
                $!State = $memento.getSavedState();
                say "Originator: State after restoring from Memento: " ~ $!State;
        }

        class Memento {
                has Str $!State;

                submethod BUILD(Str $!State) {
                }
                method getSavedState() returns Str {
                        return $!State;
                }
        }
}

class Caretaker {
        my @savedStates;

        method main() {
                my Originator $originator = Originator.new();
                $originator.set("State1");
                $originator.set("State2");
                @savedStates.push($originator.saveToMemento());
                $originator.set("State3");
                @savedStates.push($originator.saveToMemento());
                $originator.set("State4");
                $originator.restoreFromMemento(@savedStates.pop);
        }
}

my Caretaker $caretaker = Caretaker.new();
$caretaker.main();