Queue: process items in arrival order

1 min read

A queue removes the oldest item first. Use it for work waiting to be processed.

Import: import system.collections; · Availability: desktop, browser, and Node.

import system;
import system.collections;

fun main() {
    let jobs = Queue<string>();
    jobs.enqueue("first");
    jobs.enqueue("second");
    System.println(jobs.dequeue().unwrap_or("empty"));
}

This prints first. enqueue adds an item. dequeue removes the oldest item and returns Option<T>. peek reads it without removing it, also returning Option<T>. An empty queue returns None.

Member	Returns	Effect
Queue<T>()	Queue<T>	Empty queue.
enqueue(value)	void	Adds an item at the back.
dequeue()	Option<T>	Removes and returns the front item.
peek()	Option<T>	Front item, left in the queue.
clear()	void	Removes every item.
.length	int	Number of items.
.capacity	int	Items that fit before the queue must grow.
is_empty()	bool	true when the queue has no items.
reserve(additional)	Result<Unit, CapacityError>	Makes room for additional more items; Err for a negative or unsupported count.

A for loop visits items from front to back without removing them. Queues also have the query helpers such as filter and any.

See all Queue signatures. Use PriorityQueue when priority should decide which item comes next.