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Answer: How to deal with undefined returned variables.

by Russ (Deacon)
on Mar 05, 2002 at 19:51 UTC ( #149483=categorized answer: print w/replies, xml ) Need Help??

Q&A > subroutines > How to deal with undefined returned variables. - Answer contributed by Russ

knight makes a good point. Fortunately, in Perl 6, there will be a defaulting operator to simplify this very problem.
A binary // operator is the defaulting operator.
That is: 
$a // $b

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is short for: 
defined($a) ?? $a :: $b

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except that the left side is evaluated only once. It will work on arrays and hashes as well as scalars. It also has a corresponding assignment operator, which only does the assignment if the left side is undefined: 
$pi //= 3;

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Perl 6 should be such fun!

Replies are listed 'Best First'.
Re: Answer: How to deal with undefined returned variables.
by rinceWind (Monsignor) on Mar 06, 2002 at 17:00 UTC
    I take it that the difference between // and || is the difference between testing truthfulness and testing definedness.

    Hence there is not difference between $a // $b and $a || $b unless $a is 0 or "".

    It doesn't sound that useful to me.

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