$ perl -Mstrict -Mwarnings -e '
use Readonly my $unprintable => 0x15;
'
Readonly version 21 required--this is only version 1.03 at /Users/ken/perl5/perlbrew/perls/perl-5.14.2_WITH_THREADS/lib/5.14.2/Exporter/Heavy.pm line 120.
BEGIN failed--compilation aborted at -e line 2.