There was a question a while ago (why C# does allow non-member functions like C++) which prompted Eric Lippert to write a blog post about the reasons why. In it, he explains:

I am asked "why doesn t C# implement feature X?" all the time. The answer is always the same: because no one ever designed, specified, implemented, tested, documented and shipped that feature. All six of those things are necessary to make a feature happen. All of them cost huge amounts of time, effort and money. Features are not cheap, and we try very hard to make sure that we are only shipping those features which give the best possible benefits to our users given our constrained time, effort and money budgets.

I suspect that is probably the answer to why .Net does not ship with a priority queue - there was just not enough time, effort, money, demand(?) to implement one.

.NET 4.0 introduces a SortedSet<T> class, along with the ISet<T> interface which is implemented by SortedSet<T> and HashSet<T>. This will obviously make it simpler to implement your own PriorityQueue<T> class.

However, there is still no IQueue<T> interface, which would at least admit the need for priority queues or any other implementation than the basic BCL Queue<T>. Similarly, there s no IStack<T>.

Personally I find this lack of some of these most basic interfaces disappointing and short-sighted, especially as the design/specification/implementation/testing/documentation cost of extracting a simple interface from an existing class should be very low indeed.

public interface IQueue<T> : IEnumerable<T>, ICollection, IEnumerable
{
    T Dequeue();
    void Enqueue(T item);
    T Peek();
}

There, see? I ve done it.

This has been officially announced and is in the .NET 6 preview.

PriorityQueue<TElement, TPriority> (System.Collections.Generic) is a new collection that enables adding new items with a value and a priority. On dequeue the PriorityQueue returns the element with the lowest priority value. You can think of this new collection as similar to Queue but that each enqueued element has a priority value that affects the behavior of dequeue.

The following sample demonstrates the behavior of PriorityQueue<string, int>.

// creates a priority queue of strings with integer priorities
var pq = new PriorityQueue<string, int>();

// enqueue elements with associated priorities
pq.Enqueue("A", 3);
pq.Enqueue("B", 1);
pq.Enqueue("C", 2);
pq.Enqueue("D", 3);

pq.Dequeue(); // returns "B"
pq.Dequeue(); // returns "C"
pq.Dequeue(); // either "A" or "D", stability is not guaranteed.

As of January 2021, .Net Core added a PriorityQueue implementation. The actual commit to the repo and the API can be found here: https://github.com/dotnet/runtime/commit/826aa4f7844fd3d48784025ec6d47010867baab4

It s available as part of .NET6 now. Check out the following blog post for implementation.

https://dotnetcoretutorials.com/2021/03/17/priorityqueue-in-net/

See this: Add PriorityQueue to Collections, they take farking 5 years, still no PriorityQueue.