projekt kivitendo

=item cross BLOCK ARRAY ARRAY

Evaluates BLOCK for each combination of elements in ARRAY1 and ARRAY2

and returns a new list consisting of BLOCK's return values.

The two elements are set to $a and $b.

Note that those two are aliases to the original value so changing them

will modify the input arrays.

  # append each to each

  @a = qw/a b c/;

  @b = qw/1 2 3/;

  @x = pairwise { "$a$b" } @a, @b;

  # returns a1, a2, a3, b1, b2, b3, c1, c2, c3

As cross expects an array but returns a list it is not directly chainable

at the moment. This will be corrected in the future.

=cut

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;

}