$ 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]