Bug Queue never equals another queue

Relatively new to Unity, apologies if I'm missing something but I've tried many different ways to get a queue to equal another queue. No matter if I use == or .Equals it never works. I want to compare two string or char queues but even when I try int it fails. Example using int queue below:

private Queue<int> q1 = new Queue<int>();
private Queue<int> q2 = new Queue<int>();
private Queue<int> q3 = new Queue<int>();

// Start is called before the first frame update
void Start()
{

q1.Enqueue(1);
q2.Enqueue(1);
q2.Enqueue(2);
q3.Enqueue(1);

if (q1.Equals(q2))
Debug.Log("The queues q1 and q2 are equal.");
else
Debug.Log("The queues q1 and q2 are not equal." );

if (q1.Equals(q3))
Debug.Log("The queues q1 and q3 are equal.") ;
else
Debug.Log("The queues q1 and q3 are not equal." );
}

not equal is returned both times.

Am I missing something or is there a bug?

Thanks

 

If you're trying to compare values, then you need to compare the value that you would pull from the queue, not the queue itself.

The queues can't ever be equal. Queues are reference types, even if the values stored inside are value types.
It's like having two boxes and asking if they are the same box, which they aren't. Vs pulling a number 1 from each box and asking if the number is the same value, which it is.

Thus the difference between value types and ref types.

 

@Brathnann is bang on. To compare two queues, you need to iterate through them in lockstep and compare their elements. Here's one way to do this:

Code (CSharp):

1. bool AreEqual(Queue<int> q1, Queue<int> q2)
2. {
3.     if (q1.Count != q2.Count)
4.     {
5.         return false;
6.     }
7.  
8.     return Enumerable
9.         .Zip(q1, q2, (a, b) => (a, b))
10.         .All(pair => pair.a == pair.b);
11. }

(this uses Linq, so the usual caveats apply)

 

Thanks, clearly all the examples I've looked at are wrong !

 

I would suggest an extension method like this:

Code (CSharp):

1.  
2.     using System.Collections.Generic;
3.  
4.     public static class IEnumerableExtensions
5.     {
6.         public static bool ContainsEqualElements<T>(this IEnumerable<T> aFirst, IEnumerable<T> aSecond)
7.         {
8.             return ContainsEqualElements(aFirst, aSecond, EqualityComparer<T>.Default);
9.         }
10.         public static bool ContainsEqualElements<T>(this IEnumerable<T> aFirst, IEnumerable<T> aSecond, IEqualityComparer<T> aComparer)
11.         {
12.             if (aFirst == null || aSecond == null || aComparer == null)
13.                 throw new System.ArgumentNullException();
14.             var I1 = aFirst.GetEnumerator();
15.             var I2 = aSecond.GetEnumerator();
16.             bool I1HasElements, I2HasElements;
17.             do
18.             {
19.                 I1HasElements = I1.MoveNext();
20.                 I2HasElements = I2.MoveNext();
21.             }
22.             while (I1HasElements && I2HasElements && aComparer.Equals(I1.Current, I2.Current));
23.             if (I1HasElements || I2HasElements)
24.                 return false;
25.             return true;
26.         }
27.         public static bool ContainsEqualElements<T>(this IEnumerable<T> aFirst, IEnumerable<T> aSecond, System.Func<T,T,bool> aComparison)
28.         {
29.             if (aFirst == null || aSecond == null || aComparison == null)
30.                 throw new System.ArgumentNullException();
31.             var I1 = aFirst.GetEnumerator();
32.             var I2 = aSecond.GetEnumerator();
33.             bool I1HasElements, I2HasElements;
34.             do
35.             {
36.                 I1HasElements = I1.MoveNext();
37.                 I2HasElements = I2.MoveNext();
38.             }
39.             while (I1HasElements && I2HasElements && aComparison(I1.Current, I2.Current));
40.             if (I1HasElements || I2HasElements)
41.                 return false;
42.             return true;
43.         }
44.     }
45.  

It can compare any two enumerables and returns true if and only if they have the same number of elements in the same order. So it works on arrays, Lists or Queues.

Just to make this clear: If any of the two queues have more elements than the other, it will return false. So they have to contain the same number of elements and the sequence has to be the same. Optionally you can provide your own comparer or comparison callback. So it can be easily adapted to work with custom types which may require special comparison handling.

With this static class in your project you can simply do

Code (CSharp):

1. if (q1.ContainsEqualElements(q2))

Since everything is based on IEnumerable you can also check an array against a List or a List against a queue. It would always work as long as the two enumerables produces the same sequence of elements.

Spoiler: An even more exotic usecase

Code (CSharp):

1.  
2.     IEnumerable<int> MySequence()
3.     {
4.         yield return 1;
5.         Debug.Log("Matched first");
6.         yield return 4;
7.         Debug.Log("Matched first and second");
8.         yield return 7;
9.         Debug.Log("Matched first 3 elements");
10.         yield return 2;
11.         Debug.Log("All matched");
12.     }
13.    
14.     // [ ... ]
15.    
16.     if (q1.ContainsEqualElements(MySequence()))

This would give you feedback how far the comparison went Note that this is not a Unity coroutine but just an ordinary generator function. Unity is just using those to implement coroutines. This is what they are actually made for. They "generate" values, that's why they are called a generator.

 

Thanks for all the tips I have a working solution now.

 

That's just a hand-rolled Enumerable.SequenceEqual, is it not?

So really the solution to OP's problem is to replace:

Code (csharp):

1. if (q1.Equals(q2))

with

Code (csharp):

1. if (q1.SequenceEqual(q2))

And remember to import Linq.

 

Yes, you're right I barely use Linq, especially since it's always a black box and you don't know how it's implemented. But yes, in this case it's probably fine. Also the extension name is much better