-sub cross(&\@\@) {
- my $op = shift;
- use vars qw/@A @B/;
- local (*A, *B) = @_; # syms for caller's input arrays
-
- # Localise $a, $b
- my ($caller_a, $caller_b) = do {
- my $pkg = caller();
- no strict 'refs';
- \*{$pkg.'::a'}, \*{$pkg.'::b'};
- };
-
- local(*$caller_a, *$caller_b);
-
- # This map expression is also the return value.
- map { my $a_index = $_;
- map { my $b_index = $_;
- # assign to $a, $b as refs to caller's array elements
- (*$caller_a, *$caller_b) = \($A[$a_index], $B[$b_index]);
- $op->(); # perform the transformation
- } 0 .. $#B;
- } 0 .. $#A;
-}
-