$ perl -le " use warnings; use strict; my $foo; $foo++; print $foo "
1


##</code><code>##

[03:41:08.755] var noauto = [ 0, 1 ]; noauto[ 6 ] = 66; noauto ;
[03:41:08.764] [0, 1, , , , , 66]
[03:43:06.834] noauto[2].failToAutoVivify = 12; noauto;
[03:43:06.843] TypeError: noauto[2] is undefined

##</code><code>##

$ perl -MData::Dump -le " my $auto = [ 0, 1 ]; $$auto[6]=66; dd $auto; "
[0, 1, undef, undef, undef, undef, 66]


$ perl -MData::Dump -wle " my $auto = [ 0, 1 ]; $$auto[6]=66; $$auto[2]{VIVIFY}=12; dd $auto; "
[0, 1, { VIVIFY => 12 }, undef, undef, undef, 66]