I suspect autovivification.

Minimal example:

use strict;
use warnings;
my @sorted = sort { $a->[1] <=> $b->[1] } (undef, undef, undef);

[download]
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re: Sorting array, getting modification of read-only value error by tobyink
in thread Sorting array, getting modification of read-only value error by myelinviolin

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