or download this
perl -MDevel::Peek -le 'for my $x ([1]->[0]) {Dump $x; $x = pack "I",
+$x; Dump $x}' # OK
perl -MDevel::Peek -le 'my $y=1; for my $x ($y) {Dump $x; $x = pack "I
+", $x; Dump $x}' # OK
...
perl -MDevel::Peek -le 'for my $x ("1") {Dump $x; $x = pack "I", $x; D
+ump $x}' # Error, read-only
perl -MDevel::Peek -le 'for my $x (1) {Dump $x; $x = pack "I", $x; Dum
+p $x}' # Error, read-only