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Re: undef'ing @arrays caveat

by danger (Priest)
on Apr 20, 2002 at 16:30 UTC ( #160795=note: print w/ replies, xml ) Need Help??


in reply to undef'ing @arrays caveat

I couldn't believe what I saw at first. I just spotted a similar 'bug' in my code where one of my subroutines would return 'undef' in an array assignment statement.

This is why it is generally recommended that subroutines should use return with no arguments when the intent is to return a false value --- in scalar context it returns undef, in list context it returns an empty list.


Comment on Re: undef'ing @arrays caveat
Re: Re: undef'ing @arrays caveat
by Juerd (Abbot) on Apr 20, 2002 at 17:45 UTC

    This is why it is generally recommended that subroutines should use return with no arguments when the intent is to return a false value --- in scalar context it returns undef, in list context it returns an empty list.

    It doe not return undef in scalar context, it still returns the empty list, but that will evaluate to undef. If a sub always returns a single element, it makes no sense to use return without arguments, and return undef is much more explicitly self documenting.

    If your sub normally returns a scalar, use an explicit return undef;.
    If your sub normally returns a list with more than one element, use an explicit return ();.
    If your sub is polymorphic, return without arguments. Or do so explicitly: return wantarray ? () : undef;.

    - Yes, I reinvent wheels.
    - Spam: Visit eurotraQ.
    

      It doe not return undef in scalar context, it still returns the empty list, but that will evaluate to undef.

      I don't think this kind of distinction is particularly useful --- the docs clearly state that in scalar context a bare return returns undef ... whether that is because the empty list evaluates to undef in scalar context or that an undef is explicitly returned is not relevant to this discussion.

      Using return without args just means: return wantwarray()? () : undef; and if that is the behaviour you desire, using a bare return is clear, concise, well documented, and convenient.

      If your sub normally returns a list with more than one element, use an explicit return ();.

      I don't see how that is more explicit. Both return; and return (); are exactly the same --- calling return with no arguments --- and they both do the context sensitive polymorhpic return (undef or empty list). Your way does not seem to me to be more explicitly passing an empty list any more than print (); vs print; is more explicitly passing an empty list to the print function.

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