No, that presumes a 1-1 mapping. Some are, some aren't. It's more like this:

@new = ();
for (@old) {
  push @new, act_on($_);
}
[download]

Consider this to see the difference:

@old = (10..20);
sub act_on {
  return 1..$_;
}
[download]

The first element becomes 10 elements of output, the second becomes 11, and so on.

-- Randal L. Schwartz, Perl hacker