Reminds me of perl's autovivification, where you can even mix and match dicts, arrays, and scalars:

    $M{hello}[4]{world}[0]++

gives you:

    {
        'hello' => [
            undef,
            undef,
            undef,
            undef,
            {
                'world' => [
                    1
                ]
            }
        ]
    }