Short answer: autovivification.

When you write $#{$array}, you're asking Perl what the last index of the array is which the reference $array points to, in other words, you're using the previously undefined $array like an array reference, so Perl autovivifies an anonymous array for you. See also item 3 under Using References.

use warnings;
use strict;
use Data::Dumper;

my $array;
print Dumper($array);
print Dumper($#{$array});
print Dumper($array);

__END__

$VAR1 = undef;
$VAR1 = -1;
$VAR1 = [];

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In reply to Re: Using $# defines a variable? by haukex
in thread Using $# defines a variable? by smittypaddler

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