How do I read two items at a time in a Perl foreach loop?

Question

What I\'m looking for is something like:

@list = qw(1 2 3 4 5 6);
foreach (@list) {
  #perl magic goes here 
  print \"i: $i, j:$j\\n\";
}

Answer 1

I came up with this code to solve a similar requirement:

sub map_pairs(&\@) {
    my $op = shift;
    use vars '@array';
    local *array = shift;    # make alias of calling array

    return () unless @array;

    # Get package global $a, $b for the calling scope
    my ($caller_a, $caller_b) = do {
        my $pkg = caller();
        no strict 'refs';
        \*{$pkg.'::a'}, \*{$pkg.'::b'};
    };

    # Get index counter size.
    my $limit = $#array/2;

    # Localize caller's $a and $b
    local(*$caller_a, *$caller_b);

    # This map is also the return value
    map {
        # assign to $a, $b as refs to caller's array elements
        (*$caller_a, *$caller_b) = \($array[$_], $array[$_+1]);
        $op->();    # perform the transformation
    } 
    map { 2 * $_ } 0..$limit;  # get indexes to operate upon.
}

You use it like so:

@foo = qw( a 1 b 2 c 3 );
my @bar = map_pairs { "$a is $b" } @foo;

to get:

@bar = ( 'a is 1', 'b is 2', 'c is 3' );

I've been meaning to submit to the maintainer of List::MoreUtils, but I don't have an XS version to offer.