为什么两个类型的别名没有具有相同名称的扩展方法？

Question

在Scala 3替补中，输入以下

type B = Int

extension (a: A)
  def f() = println("A!")

extension (b: B)
  def f() = println("B!")

给出错误，

8 |  def f() = println("B")
  |      ^
  |Double definition:
  |def f(a: A)(): Unit in object rs$line$1 at line 5 and
  |def f(b: B)(): Unit in object rs$line$1 at line 8
  |have the same type after erasure.
  |
  |Consider adding a @targetName annotation to one of the conflicting definitions
  |for disambiguation.

为什么我不能这样做？

我希望在以下内容中，类型定义足以使编译器/Scala知道要使用哪种实现

val a: A = 0
val b: B = 0
val x: Int = 0

a.f() // I would expect "A!"
b.f() // I would expect "B!"
x.f() // I would expect an error

我怀疑不透明类型的别名我在寻找什么？