http://www.perlmonks.org?node_id=40240


in reply to Possible pitfall with Slices

A better way of doing this: 
@a{qw{ a b c }} = ();    # not (1)x3 or whatever

foreach (qw{ a b c }) {
  print "$_\n" if exists $a{$_};
}

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Thus we don't have to worry about being sure the values of the hash are all present and what-not. Specify an empty list on the right-hand-side to set the values all to undef, and just use exists to see if it's there. It's also slightly faster (but not much).

In Section Seekers of Perl Wisdom