wildcards + SAM = </3

[adriaanm]

class P[R]
trait MyChangeListener[T] { def changed(observable: P[_ <: T]) }

class Test {
  // type checks
  def m[S]: MyChangeListener[_ >: S] = new MyChangeListener[S] { def changed(observable: P[_ <: S]): Unit = ??? }

  // should type check too
  def l[S]: MyChangeListener[_ >: S] = (observable: P[_ <: S]) => ???
}

[adriaanm]

better support for use-site variance is something for the back log, but we should let you "variance-cast" your way to something type inference knows how to handle