On a recent worksheet I was presented with the question asking what would be the output of the following code:
class A { def m(x:Double) = x+x }
class B[Any] extends A{ def m(x: Any) = print(x) }
class C[Any] { def m (x:Double) = x+x; def m (x: Any) = print(x) }
val obj1 = new B[Int]; val obj2 = new C[Any]
obj1.m(1); obj1.m(2.3); obj2.m(4); obj2.m(5.6)
I'm quite confused as to what having a concrete type in the square brackets after the class name would mean (i.e. class B[Any]). Is the later expression val obj1 = new B[Int] valid because Int <: Any, Int being a subclass of Any?
When later running the code snippet, the result given was simply "1" being printed. This was not what I had expected the call to obj.m(2.3) to resolve at def m(x: any), where it seems in actuality the compiler went up to A and called the m in class A.
The later expressions, obj2.m(4) and obj2.m(5.6) seems to make sense as both 4 and 5.6 would land in the function with def m(x: Double), thus not print anything out.
In what order exactly does the compiler traverse to find what to call? I'd be very grateful if someone could clear up my confusions with how polymorphism is handled here by Scala, thank you very much :)