Question

The following code does not compile:

var next: (A, A) = (null, n)

Error:

error: type mismatch;
found   : Null(null)
required: A
var next: (A, A) = (null, n)

Also var next: (A, A) = ((null: A), n) fails with the same error.

Somehow I think it should compile.

I’m currently using the following code which seems to work:

var next: (A, A) = (null.asInstanceOf[A], n)

Why doesn’t it work? Bug or feature?

Edit

After reading didiers answer the problem is obvious. I missed that null can only be assigned to AnyRef types. For my problem I choose to make the tuple (n,n) and have a boolean flag whether the first entry is valid. Depending on the application Option might be a better solution.

Answer 1

Probably because your A parameter type is not guaranteed to be <: AnyRef. It should if you intend to pass null. If so, I would say feature

Edit. See Daniel’s comment below, the solution is >: Null, See AgileSteel answer too.