match tuple with null

Question

I don't understand why the following case doesn't match. Null should be an instance of Any, but it doesn't match. Can someone explain what is going on?

val x = (2, null)
x match {
    case (i:Int, v:Any) => println("got tuple %s: %s".format(i, v))
    case _ => println("catch all")
}

prints catch all

Thanks.

Answer 1

This is exactly as specified.

Type patterns consist of types, type variables, and wildcards.
A type pattern T is of one of the following forms:

* A reference to a class C, p.C, or T#C.
This type pattern matches any non-null instance of the given class.

It's interesting that so much relevance has been attributed to null being a member of Any. It's a member of every type but AnyVal and Nothing.

Answer 2

Have you tried the v placeholder for anything?

val x = (2, null)
x match {
    case (i:Int, v) => println("got tuple %s: %s".format(i, v))
    case _ => println("catch all")
}

Answer 3

That's as specified (Scala Reference 2.7, section 8.2):

A reference to a class C, p.C, or T#C. This type patternmatches any non-null instance of the given class. Note that the prefix of the class, if it is given, is relevant for determining class instances. For instance, the pattern p.C matches only instances of classes C which were created with the path p as prefix.

Answer 4

I'm just guessing here since I'm no scala expert but according to the documentation for the Any class in scala I'm thinking that since null isn't an object, it doesn't derive from Any and as such doesn't match the first listed case.

Adding the code sample below. It prints "something else" when run.

val x = (2, null)  
x match {  
    case (i:Int, v:Any) => println("got tuple %s: %s".format(i, v))  
    case (i:Int, null) => println("something else %s".format(i))
    case _ => println("catch all")  
}  

After more research it seems like null should match with any sense the documentation says that it extends AnyRef which extends Any.

EDIT: Like everyone else has said. The first case doesn't match null on purpose. It's specified in the documentation.