请教一个pseudohash相关的问题

在看《Programming Perl》3rd Edition，请教一个问题。

8.3.5. Pseudohashes

A pseudohash is any reference to an array whose first element is a reference to a hash. You can treat the pseudohash reference as either an array reference (as you would expect) or a hash reference (as you might not expect). Here's an example of a pseudohash:

$john = [ {age => 1, eyes => 2, weight => 3}, 47, "brown", 186 ];

The underlying hash in $john->[0] defines the names ("age", "eyes", "weight") of the array elements that follow (47, "brown", 186). Now you can access an element with both hash and array notations:
$john->{weight}             # Treats $john as a hashref
$john->[3]                  # Treats $john as an arrayref

我试了一下，执行 "print $john->[3];" 能得到"186"，可 "print $john->{weight};" 却提示 "Not a HASH reference"，没能按其所说的得到"186"，是为什么？

书上说是试验功能，现在看样子是取消了吧？这玩意太 bug 了