zen% cat t0
  package A; $x = bless {}; $y = bless [], $x; print "$y";

  zen% /opt/perl-5.6.1/bin/perl -wl t0
  A=HASH(0x811198c)=ARRAY(0x8111a94)

  zen% /opt/perl-5.8.0/bin/perl -wl t0
  Attempt to bless into a reference at t0 line 1.