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Program Repair Shop

18

Identity theft

        my $g = Guard->new("Fred");
        my $a1 = Alarm->new;
        $a1->add_observer($g);
        $a1->notify_observers("I like pie!");

        undef $a1;
        my $a2 = Alarm->new;
        $a2->notify_observers("I like pie!"); 

• $a2 has no observers, so the final call should do nothing

• But it happens to have the same hash key that $a1 did

• So $g is notified anyway

• This is hard to fix!

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