You wrote:

    > i tried 

    > sub flip { $@_[0] = !($@_[0] };
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So close. :) Try this:

    sub flip { ${ $_[0] } = !${ $_[0] } }
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Alternatively, check out Tie::FlipFlop on CPAN. It uses tie to automatically take care of a flipflop state, and it lets you use other values than 0 and 1, as well. It's very cool. And you also don't have to call a flip function, because tie handles it all automagically.

Here's a snippet from the docs:

    use Tie::FlipFlop;

    tie my $flipflop => Tie::FlipFlop => qw /Red Green/;

    print  $flipflop;      # Prints 'Red'.
    print  $flipflop;      # Prints 'Green'.
    print  $flipflop;      # Prints 'Red'.
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