>perl -wle"@a=1; for ((),@a) { push @a,$_+1; print }"
1

>perl -wle"@a=1; for (@a) { push @a,$_+1; print }"
1
2
3
4
...

##</code><code>##

>perl -wle"@a=(1,2); for (@a) { pop @a; print qq{<$_>} }"
<1>

>perl -wle"@a=(1,2); for ((),@a) { pop @a; print qq{<$_>} }"
<1>
Use of freed value in iteration at -e line 1.