I noticed that too, but I don’t see it documented. The closest I’ve come are two references to eliminating arrows between “brackets subscripts” — perlref#Using-References (3) and perlreftut#Arrow-Rule. Or does a pair of parentheses () also count as a “subscript”?

... does a pair of parentheses () also count as a “subscript”?

I've always assumed this is so and I've never encountered a counterexample, but this may just be because I almost always, if not always, use the
    $reference->{any}[$number]{of}[$levels]->();
form; it seems more clear and the other form makes me just a bit nervous.

Update: Perhaps my fondness for the form exemplified above has to do with the fact that I will often try to shorten and self-document my code by using intermediate variables:
    my $cr_that_does_something = $reference->{any}[$number]{of}[$levels];
    ...
    $cr_that_does_something->('foo');
    ...
    $cr_that_does_something->('bar');
The  -> arrow is, of course, always needed here (if you don't use a sigil!).

---

Give a man a fish:  <%-{-{-{-<

Some golf code can have the advantage of clarifying the question by being read quickly. It may be more for quick examples because in production code spelling things out more may make for easier debugging and modification.

It later occurred to me that you don't always need a subroutine reference to call outside an object or package although it could be useful. If the call is not object dependent you can just specify the name of the other package like "main::hello()".

I included my simplified/golfed example below:

package C;

sub new {
    my $self = shift;
    my $class = ref($self) || $self;

    return bless {sub_ref => shift}, $class;
}

sub doit {
    $_[0]->{sub_ref}();

    # you don't always need a reference to call outside of an object
    main::hello();
}

package main;

sub hello {
    print "hello\n";
}

C->new(\&hello)->doit;
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