use Tie::Array qw( );
our @ISA = 'Tie::StdArray';

sub FETCH {
   my ($self, $idx) = @_;
   warn("Fetching index $idx\n");
   return $self->SUPER::FETCH($idx);
}

my @a;
tie @a, __PACKAGE__;
$#a = 4;

my $s;
$s = $a[-@a+1];  # Fetching index 1
$s = $a[-@a];    # Fetching index 0
$s = $a[-@a-1];  # FETCH not called!

$s = $a[@a];     # Fetching index 5