Imported From: https://issues.scala-lang.org/browse/SI-490?orig=1
Reporter: @blair

@SethTisue said:
I find I am hitting this issue in my own code. +1 on an eventual fix; Scala has taken a step backward from Java in this respect.

Lauri Alanko (lealanko) said:
There is a similar issue for classOf[]. Whereas the type of getClass() is currently too weak, the type of classOf[] is too strong:

scala> classOf[List[int]]
res4: java.lang.Class[List[int]] = class scala.List

scala> classOf[List[String]]
res5: java.lang.Class[List[String]] = class scala.List

That is, the type system claims that the class object is a representation of a type application, even though there is no real run-time information about the type argument.

I think it would be desirable for the property to hold that if (a : Class[A]) eq (b : Class[B]), then A <: B <: A. This is not currently true.

So I suggest that classOf gets the same treatment as is suggested for getClass: let the type of classOf[A] be Class[B] where B is the "existential erasure" of A (or whatever is the upper bound of all types that share the erasure of A), i.e.:

classOf[List[A]] : Class[List[T] forSome { type T }]

@SethTisue said:
see also #4696

Commit Message Bot (anonymous) said:
(extempore in r25137) A total rewrite of "runtimeClass", discarding the user-space
approach in favor of simply fixing getClass.

def f1 = 5.getClass // Class[Int]
def f2 = (5: AnyVal).getClass // Class[_ <: AnyVal]
def f3 = (5: java.lang.Integer).getClass // Class[_ <: java.lang.Integer]

class A
class B extends A

def f1 = (new B: Any).getClass().newInstance() // Any
def f2 = (new B: AnyRef).getClass().newInstance() // AnyRef
def f3 = (new B: A).getClass().newInstance() // A
def f4 = (new B: B).getClass().newInstance() // B

But that's not all!

def f0[T >: B] = (new B: T).getClass().newInstance()

def f5 = f0[Any] // Any
def f6 = f0[AnyRef] // AnyRef
def f7 = f0[A] // A
def f8 = f0[B] // B

Closes #490, #896, #4696. Review by moors. (Note: I think this is
pretty good, but picky review requested.)