After looking at this in the morning I realized I'm keying with hashcodes which is not guaranteed to be unique.

@AustinSmith13 let me know if you fix the uniqueness problem and I'll review. Thanks for the PR! 👍

@jacksondunstan After a little bit of research object.GetHashCode() returns a unique index assigned to the object by the CLR when the object is created and released from garbage collection.

So I don't think its likely to have a hash-code duplicate in the same app-domain but maybe after collection which I don't think is a problem.

I did implement a version with hash collision handling but it less nice looking and is probably slower. (but not by much)

I am thinking about keeping it the way it is, but microsoft advises against it here https://docs.microsoft.com/en-us/dotnet/api/system.object.gethashcode?view=netframework-4.8

public static int GetHandle(object obj)
{
	// Null is always zero
	if (object.ReferenceEquals(obj, null))
	{
		return 0;
	}
				
	lock (objects)
	{
		// Look up the handle in the hash table
		uint hash = (uint)obj.GetHashCode();
		List<int> handleBucket = null;
		if (handleBucketByHash.TryGetValue(hash, out handleBucket))
		{
			for (int i = 0; i < handleBucket.Count; i++)
			{
				int handleInBucket = handleBucket[i];
				object objectInBucket = objects[handleInBucket];
							
				if (object.ReferenceEquals(objectInBucket, obj))
				{
					return handleInBucket;
				}
			}
		}
	}
				
	// Object not found
	return Store(obj);
}

I've tried to cause hash collisions by creating and destroying thousands of objects per frame. No collisions.

If you are fine with whats there I would like to keep it the way it is without any collision handling for slight performance benefit.

Sorry about constantly changing this I can't help but try to make things perfect. I realize a better way of doing this would be to use a single dictionary Dictionary<object, int>. Dictionaries already consider hash collisions for there keys. I'll have this change ready for review later today.

@jacksondunstan This is ready for review.

After looking into how dictionaries work, I realized they already do everything I was previously trying to do. Internally they call GetHashCode and check equality for collisions.