DB<76> sub change { $_[0] = 666 }

  DB<77> $a=42

  DB<78> change($a)

  DB<79> p $a
666
  DB<80> change(42)
Modification of a read-only value attempted at (eval 86)[c:/Perl_524/lib/perl5db.pl:737] line 2.

  DB<81>

##</code><code>##

  DB<81> sub change_arr { $_[0] = [666] }

  DB<82> $a=[42]

  DB<83> change_arr($a)

  DB<84> x $a
0  ARRAY(0x3363180)
   0  666
  DB<85> change_arr([42]) #NO ERROR???

  DB<86>