Immutable Collections

ImmutableQueueDemo.cs

	//uses nuget System.Immutable.Collections
	//using System.Immutable.Collections;

	//On an implementation level, an ImmutableQueue is a linked list with head and tail pointers. So q is a reference to an empty list.
	var q = ImmutableQueue<int>.Empty; //[]

	//Create a new node, and point it towards the list 'q' (which is empty)
	var q1 = q.Enqueue(1);  // 1. 

	//Create a new node, and point it towards the list 'q1' (which is empty)
	var q2 = q1.Enqueue(2);     // 2 -> q1 (which is equivalent to): 2 -> 1

	//Not as smart as could be: Equivalent queues are not reference equal	
	var q2copy = q1.Enqueue(2);	// equivalent to q2, but not reference equal
	var isRefEqual1 = (q2 == q2copy); //returns false
	Console.WriteLine($"q2 is {(isRefEqual1 ? "" : "not " )}equal to q2copy");

	//However, all empty Queues share a reference.
	var qCopy = q.Enqueue(3).Dequeue(); 	//Add 3 to the empty queue, then dequeue it, ending with an empty queue
	var isRefEqual2 = (q == qCopy); 		//returns true
	Console.WriteLine($"q is {(isRefEqual2 ? "" : "not ")}equal to qcopy");

	Console.WriteLine($"State: q-Node count: {q.Count()}, q1-Node count: {q1.Count()}, q2-Node count: {q2.Count()}");

	q.Enqueue(100); //has no effect: Returns a new Queue, doesn't change existing one.
	q.Enqueue(100); //has no effect: Returns a new Queue, doesn't change existing one.

	Console.WriteLine($"State: q-Node count: {q.Count()}, q1-Node count: {q1.Count()}, q2-Node count: {q2.Count()}");

	q1.Dequeue(); //has no effect: Returns a new Queue, doesn't change existing one.
	q1.Dequeue(); //has no effect: Returns a new Queue, doesn't change existing one.

	Console.WriteLine($"State: q-Node count: {q.Count()}, q1-Node count: {q1.Count()}, q2-Node count: {q2.Count()}");