You could be so much lazier.

#!/usr/bin/perl
use strict;
use warnings;
use Tie::Array;

package Tie::Array::LastAccessed;
use base qw( Tie::StdArray );

my %last_accessed;

for my $methname ( qw( STORE FETCH ) ) {
    my $supername = "SUPER::$methname";
    my $glob = do { no strict 'refs'; \*{ $methname } };
    *$glob = sub {
        my $self = shift;
        my ( $idx ) = @_;
        $last_accessed{ 0 + $self } = $idx;
        $self->$supername( @_ );
    };
}

sub which {
    my $self = shift;
    $last_accessed{ 0 + $self };
}

sub what {
    my $self = shift;
    $self->FETCH( $last_accessed{ 0 + $self } );
}

sub DESTROY {
    my $self = shift;
    delete $last_accessed{ 0 + self };
    $self->SUPER::DESTROY();
}

1;
[download]