koobas.hobune.stream
List of Quaternions - NullReferenceException with types or type check errors without?
I'm trying to create a list of quaternions. I need to be able to add and remove quaternions at any time, so I don't want to use an Array. But I seem to be getting NullReferenceExceptions no matter what I do.
Here's a simple example:
q = Quaternion(1, 0, 0, 0)
print(q.ToString()) # Works fine
qList = [] as List[of Quaternion]
qList.Add(q) # Crashes here with NullReferenceException: Object reference not set to an instance of an object.
Here's another example:
q = Quaternion(1, 0, 0, 0)
print(q.ToString()) # Works fine
qList = [q] as List[of Quaternion]
print(qList.ToString()) # Crashes here with NullReferenceException: Object reference not set to an instance of an object.
Note that if I remove as List[of Quaternion] from that second example, it works, but then the compiler only sees qList as a list, so the following then doesn't work:
def methodThatTakesQList(qList as List[of Quaternion]:
print(qList.ToString())
q = Quaternion(1, 0, 0, 0)
print(q.ToString()) # Works fine
qList = [q]
methodThatTakesQList(qList) # The best overload for the method 'methodThatTakesQList(Boo.Lang.List[of UnityEngine.Quaternion])' is not compatible with the argument list '(Boo.Lang.List)'.
If I remove the as List[of Quaternion], this example perfectly works too, but I'd like to actually use some methods of quaternions (IE, multiplying them together) which fails the compilation type-check, since it sees it as me just trying to multiply objects together.
I'm finding that it's best to just avoid lists altogether... they cause an unnecessary impact on performance and a lot of Unity just doesn't seem to play nicely with them.
For further questions that are boo related, you might want to include something like [boo] in the title. Boo questions are quite rare, so if there are people around that actually use boo, it's unlikely that this person will click on your question.
What you are doing there makes not much sense. A List and an array are two seperate things. What you do here is creating an array and then use the as-cast to cast it into a List. However since an array is not a List this cast will fail. And one of the properties of the as-cast is that it will return null if a cast is not possible.
I'm not familiar with boo at all (like most people here). However from what i read the as-cast works the same as in all .NET / Mono languages.
What you actually want is creating an instance of a List. This should look like this:
qList = List[of Quaternion]()
Usually the generic List also has a ToArray method if you need a built-in array from that list. However since boo has it's own List implementation it might be different.
edit
Little correction ;) the [] brackets seem to create an untyped List and not an array. Anyways the same problem: a List is not a List[of Quaternion] so an as cast will fail.
Thank you! I hit this same problem again months later and was going to post a new question, meanwhile thinking it has seemed like I had asked about this before. Checked my list of asked questions and lo and behold, I had! Tried your solution and it worked! Thanks!
