Range Over Channels in Perl

In a previous example, we saw how foreach provides iteration over basic data structures. We can also use this syntax to iterate over values received from a channel-like construct in Perl.

use strict;
use warnings;
use Thread::Queue;

my $queue = Thread::Queue->new();

# We'll iterate over 2 values in the $queue.
$queue->enqueue("one");
$queue->enqueue("two");
$queue->end();

# This while loop iterates over each element as it's
# received from $queue. Because we called end() on the
# queue above, the iteration terminates after
# receiving the 2 elements.
while (defined(my $elem = $queue->dequeue())) {
    print "$elem\n";
}

To run the program:

$ perl range-over-channels.pl
one
two

This example also showed that it’s possible to end a non-empty queue but still have the remaining values be received.

In Perl, we don’t have built-in channels like in some other languages, but we can use the Thread::Queue module to achieve similar functionality. The Thread::Queue provides a thread-safe FIFO queue which can be used to pass data between threads.

Here’s a breakdown of the Perl equivalent:

1. We use Thread::Queue->new() to create a new queue.
2. We add elements to the queue using the enqueue method.
3. We call end() on the queue to signal that no more items will be added.
4. We use a while loop to dequeue and process items until the queue is empty.
5. The dequeue method returns undef when the queue is empty and has been ended, which terminates our loop.

This approach provides a way to iterate over a channel-like structure in Perl, similar to ranging over channels in other languages.