$x->[0] = 1 # 1 for $x->[0]; () # '', undef, [ 1 ] # +fetch
$x->[0] = 1 # 1 for $x->[1]; () # '', undef, [ 1, undef ] # +fetch
$x->[0] = 1 # 1 for $x->[0]; () # '', undef, [ 1 ] # +fetch
$x->[0] = 1 # 1 for $x->[1]; () # '', undef, [ 1, undef ] # +fetch