http://qs1969.pair.com?node_id=1134310

hurricup has asked for the wisdom of the Perl Monks concerning the following question:

Encountered an interesting piece of code inside of ExtUtils::Constant::Base:

my $l = ref $a eq 'ARRAY' ? ($a->[0] || $->[1]) : $a;
The question is about $->1. According to perlvar $- is a The number of lines left on the page of the currently selected output channel. And what are we doing here? Comparing lines number with anonymous array? What the..?

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Re: The mystery of $->[1]
by kcott (Bishop) on Jul 11, 2015 at 20:59 UTC

    G'day hurricup,

    ++ Good catch!

    The code itself parses as legal Perl:

    $ perl -MO=Deparse,-p -e 'my $l = ref $a eq "ARRAY" ? ($a->[0] || $->[ +1]) : $a;' (my $l = ((ref($a) eq 'ARRAY') ? ($a->[0] || ($- > [1])) : $a)); -e syntax OK

    And, as you can see, your analysis is correct: '$-' is being compared with '[1]'.

    There's actually two adjacent lines like that in the source code:

    # Deal with the case of an item actually being an array ref to 1 o +r 2 # hashrefs. Don't assign to $a or $b, as they're aliases to the or +ignal my $l = ref $a eq 'ARRAY' ? ($a->[0] || $->[1]) : $a; my $r = ref $b eq 'ARRAY' ? ($b->[0] || $->[1]) : $b;

    I suspect those should be:

    my $l = ref $a eq 'ARRAY' ? ($a->[0] || $a->[1]) : $a; my $r = ref $b eq 'ARRAY' ? ($b->[0] || $b->[1]) : $b;

    although, I haven't delved deeply enough into the code to say for certain.

    I suggest you raise a bug report for this.

    -- Ken

      Thought about typo, but last my "discoveries" shown that I'm John Snow in Perl :) And thought it may be some unknown magic.

      Will report a bug.

Re: The mystery of $->[1]
by LanX (Sage) on Jul 11, 2015 at 20:56 UTC
    Obviously a typo ('a' missing), which isn't caught by the parser because of your wtf interpretation.

    Cheers Rolf
    (addicted to the Perl Programming Language and ☆☆☆☆ :)
    Je suis Charlie!

    PS: you might want to report the bug.