Perl treats a negative array subscript as an offset from the end. Given
this, the preferred way to get the last element is $x[-1], not
$x[$#x] or $x[@x-1], and the preferred way to get the next-to-last
is $x[-2], not $x[$#x-1 or $x[@x-2].
The biggest argument against the non-preferred forms is that <B>their
semantics changeB> when the computed index becomes negative. If @x
contains at least two elements, $x[$#x-1] and $x[@x-2] are
equivalent to $x[-2]. But if it contains a single element,
$x[$#x-1] and $x[@x-2] are both equivalent to $x[-1]. Simply
put, the preferred form is more likely to do what you actually want.
As Conway points out, the preferred forms also perform better, are more
readable, and are easier to maintain.
This policy notices all of the simple forms of the above problem, but
does not recognize any of these more complex examples:
my $ref = \@arr; $ref->[$#arr];