Range Over Channels in Squirrel

In a previous example, we saw how for loops provide iteration over basic data structures. In Java, we can use similar constructs to iterate over elements received from a queue.

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

public class RangeOverQueue {
    public static void main(String[] args) throws InterruptedException {
        // We'll iterate over 2 values in the queue.
        BlockingQueue<String> queue = new LinkedBlockingQueue<>(2);
        queue.put("one");
        queue.put("two");

        // This loop iterates over each element as it's received from queue.
        // Because we don't add more elements, the iteration terminates
        // after receiving the 2 elements.
        while (!queue.isEmpty()) {
            String elem = queue.take();
            System.out.println(elem);
        }
    }
}

When you run this program, you’ll see:

$ javac RangeOverQueue.java
$ java RangeOverQueue
one
two

This example demonstrates how to iterate over elements in a queue. In Java, we use a BlockingQueue which is similar to a channel in other languages. The while loop continues until the queue is empty, which is analogous to ranging over a channel until it’s closed.

Note that in Java, we don’t have the concept of closing a queue like we do with channels in some other languages. Instead, we simply stop adding elements and continue processing until the queue is empty. If you need to signal that no more elements will be added, you might use a separate boolean flag or a poison pill object.