Let's continue our series on new .NET 6 features with an interesting new way to order objects: PriorityQueue<T, N>!

Current Implementation

.NET 5 and prior have a class called Queue<T>, which represents a collection with first-in, first-out (FIFO) behavior. This is roughly the kind of behavior that might happen when people stand in a line; people exit the line in the order they joined it.

A group of people stand in a line outside a popular restaurant.
"...How long till we get a table?" Photo by John Tuesday / Unsplash

When objects are added to the queue (or "enqueued"), they are removed from it (or "dequeued") in the same order as they were added.

Queue<string> names = new Queue<string>();

names.Dequeue(); //Alex
names.Dequeue(); //Leah
names.Dequeue(); //Haley

New Implementation

.NET 6 introduces a new class, PriorityQueue<T, N>, which behaves similarly to a Queue<T>, except each item in a PriorityQueue<T, N> also has an order assigned (represented by N). Items are then dequeued in the order specified by the N value, not solely by first-in, first-out.

PriorityQueue<string, int> priorityWords = new();

priorityWords.Enqueue("Leah", 2);
priorityWords.Enqueue("Harvey", 4);
priorityWords.Enqueue("Haley", 3);
priorityWords.Enqueue("Alex", 1);

Console.WriteLine(priorityWords.Dequeue()); //Alex
Console.WriteLine(priorityWords.Dequeue()); //Leah
Console.WriteLine(priorityWords.Dequeue()); //Haley
Console.WriteLine(priorityWords.Dequeue()); //Harvey

In a PriorityQueue<T, N>, the order value can be any primitive type. Assume we have an enumeration called ShowRating:

public enum ShowRating
    Transcendant, //1
    Amazing, //2
    Good, //3
    OK //4

We could use that enum as the order value in a PriorityQueue<T, N> to rank a bunch of tv shows.

var tvShows = new PriorityQueue<string, ShowRating>();

tvShows.Enqueue("Modern Family", ShowRating.Good);
tvShows.Enqueue("Ted Lasso", ShowRating.Amazing);
tvShows.Enqueue("MasterChef", ShowRating.Good);
tvShows.Enqueue("Breaking Bad", ShowRating.Transcendant);
tvShows.Enqueue("Happy Endings", ShowRating.Amazing);
tvShows.Enqueue("Game of Thrones (Seasons 1-6)", ShowRating.Amazing);
tvShows.Enqueue("Game of Thrones (Seasons 7-8)", ShowRating.OK);
tvShows.Enqueue("How to Get Away with Murder", ShowRating.Good);
tvShows.Enqueue("Hell's Kitchen", ShowRating.OK);

Console.WriteLine("What should we watch?");
var currentShow = tvShows.Dequeue();

//The shows will be dequeued in order of the ShowRating value
Console.WriteLine($"Let's try {currentShow}!");

while(tvShows.Count > 0)
    Console.WriteLine($"If not, let's try {tvShows.Dequeue()}.");
Given this code, which show will be listed first?

Demo Project

As with all posts in this series, there is a demo project you can check out over on GitHub that shows these examples of PriorityQueue<T, N> so you can run them and see the output. Check it out!

GitHub - exceptionnotfound/NET6BiteSizeDemos
Contribute to exceptionnotfound/NET6BiteSizeDemos development by creating an account on GitHub.

Happy Coding!