3.  Subroutine calls and lookups of individual array elements arise
    often enough that it gets cumbersome to use method 2. As a form of
    syntactic sugar, the examples for method 2 may be written:
        $arrayref->[0] = "January";   # Array element
        $hashref->{"KEY"} = "VALUE";  # Hash element
        $coderef->(1,2,3);            # Subroutine call

    The left side of the arrow can be any expression returning a
    reference, including a previous dereference. Note that `$array[$x]'
    is *not* the same thing as `$array->[$x]' here:

        $array[$x]->{"foo"}->[0] = "January";

    This is one of the cases we mentioned earlier in which references
    could spring into existence when in an lvalue context. Before this
    statement, `$array[$x]' may have been undefined. If so, it's
    automatically defined with a hash reference so that we can look up
    `{"foo"}' in it. Likewise `$array[$x]->{"foo"}' will automatically
    get defined with an array reference so that we can look up `[0]' in
    it. This process is called *autovivification*.