return (); is the same as return;, which returns an empty list when the sub is called in list context and a false value when the sub is called in scalar context. On the other hand, return undef; always returns one value from the sub: undef. When that sub is called in list context, it returns a list consisting of one element (undef). Because that list has one element, when you evaluate it in boolean context, it's true! See also Perl::Critic::Policy::Subroutines::ProhibitExplicitReturnUndef.

In reply to Re: What could make "()" a good value for boolean false? by Anonymous Monk
in thread What could make "()" a good value for boolean false? by morgon

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