Queue<E> class Null safety

A Queue is a collection that can be manipulated at both ends. One can iterate over the elements of a queue through forEach or with an Iterator.

It is generally not allowed to modify the queue (add or remove entries) while an operation in the queue is being performed, for example during a call to forEach. Modifying the queue while it is being iterated will most likely break the iteration. This goes both for using the iterator directly, or for iterating an Iterable returned by a method like map or where.

Example:

final queue = Queue<int>(); // ListQueue() by default
print(queue.runtimeType); // ListQueue

// Adding items to queue
queue.addAll([1, 2, 3]);
queue.addFirst(0);
queue.addLast(10);
print(queue); // {0, 1, 2, 3, 10}

// Removing items from queue
queue.removeFirst();
queue.removeLast();
print(queue); // {1, 2, 3}