sub matrixGet {
        my ($o, $x, $y, $z) = @_;
        return $o->{m}[$x][$y][$z];
    }
    sub matrixSet {
        my ($o, $x, $y, $z, $val) = @_;
        $o->{m}[$x][$y][$z] = $val;
    }
    ...
    $o->matrixGet(@{$h{$key}});
    $o->matrixSet(@{$h{$key}},5);