in reply to Re^2: Do I need to use defined?
in thread Do I need to use defined?

In Perl, three things are false: the undefined value (undef), the empty string (''), and zero (0). Two of those things are defined.

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Re^4: Do I need to use defined?
by afoken (Chancellor) on Sep 07, 2017 at 06:49 UTC

    Empty arrays and hashes are also false:

    >perl -E 'my @a=(); my @a2=@a or say "FALSE"'
FALSE

>perl -E 'my %h=(); my %h2=%h or say "FALSE"'
FALSE

>perl -E 'my @a=(0); my @a2=@a or say "FALSE"'

>perl -E 'my %h=(""=>0); my %h2=%h or say "FALSE"'

>

    [download]

    Alexander

    --
    Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
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      Empty arrays and hashes become zero in scalar context, and zero is false.
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        ...

        Read my posting again. I'm using list context in both cases.

        Or just read "Truth and Falsehood" in perlsyn:

        The number 0, the strings '0' and "" , the empty list () , and undef are all false in a boolean context. All other values are true. Negation of a true value by ! or not returns a special false value. When evaluated as a string it is treated as "" , but as a number, it is treated as 0. Most Perl operators that return true or false behave this way.

        Alexander

        --
        Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
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