$a = []; $b = undef; $d ={}; $r = []; $c ={}; $a->[0] = $c; $a->[2]= $r; $$c{1} =15; $$c{0} = 20; $$c{2} =$a; $$c{3} = $b; $$c{'foo:bar'} = $d; $$c{thing} = $r; $$d{10} = $r; $$d{a123} = $r; $$d{5} = []; $a