require Bounded_Array;
tie @ary, 'Bounded_Array', 2;   # maximum allowable subscript is 2
$| = 1;
for $i (0 .. 10) {
    print "setting index $i: ";
    $ary[$i] = 10 * $i;       # should raise exception on 3
    print "value of element $i now $ary[$i]\n";
}
*****
package Bounded_Array;
use Carp;
use strict;
*****
sub TIEARRAY {
    my $class = shift;
    my $bound = shift;

    confess "usage: tie(\@ary, 'Bounded_Array', max_subscript)"
        if @_ or $bound =~ /\D/;

    return bless {
        BOUND => $bound,
        ARRAY => [],
    }, $class;
}
*****
sub FETCH {
    my ($self, $idx) = @_;
    if ($idx > $self->{BOUND}) {
        confess "Array OOB: $idx > $self->{BOUND}";
    }
    return $self->{ARRAY}[$idx];
}
*****
sub STORE {
    my ($self, $idx, $value) = @_;
    if ($idx > $self->{BOUND} ) {
        confess "Array OOB: $idx > $self->{BOUND}";
    }
    return $self->{ARRAY}[$idx] = $value;
}
*****
setting index 0: value of element 0 now 0
setting index 1: value of element 1 now 10
setting index 2: value of element 2 now 20
setting index 3: Array OOB: 3 > 2 at Bounded_Array.pm line 39
        Bounded_Array::FETCH called at testba line 12