You'd be wanting this I expect... 
  sub flip { ${$_[0]} = !${$_[0]} };

[download]
The precedence of de-reference $ and array subscript [] mean that what you wrote doesn't work. You need those ${ ... } de-reference brackets for all de-references except the simplest.

Note also that you meant $_[0] rather than @_[0] didn't you ;-)

Interestingly 

  sub flip { $$_[0] = !($$_[0]) }

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Isn't a syntax error and doesn't produce any warnings but does something completely unintended. 
  perl -w -e 'use strict; sub flip { $$_[0] = !($$_[0]) }; my $z=1; fl
+ip(\$z); print "$z\n"'
  1

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I don't understand why this doesn't print use of unitialised variable or something like that...

In reply to Re: something about improving code... by ncw
in thread something about improving code... by Buckaroo Buddha

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