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// record the status quo after this fix
// not clear to @adriaanm why an upper-bounded existential in an invariant position
// is different from putting that upper bound in a covariant position
object Test1 {
trait Ext[T]
implicit def f[A, Coll <: CC[A], CC[X] <: Traversable[X]](implicit xi: Ext[A]): Ext[Coll] = ???
implicit val m: Ext[List[List[Int]]] = new Ext[List[List[Int]]]{}
implicitly[Ext[List[Int]]] // fails - not found
implicitly[Ext[List[List[Int]]]] // compiles
implicitly[Ext[List[List[List[Int]]]]] // fails - not found
// Making Ext[+T] should incur the same behavior as these. (so says @paulp)
implicitly[Ext[_ <: List[Int]]] // compiles
implicitly[Ext[_ <: List[List[Int]]]] // fails - ambiguous
implicitly[Ext[_ <: List[List[List[Int]]]]] // compiles
// But, we currently get:
trait ExtCov[+T]
implicitly[ExtCov[List[Int]]] // fails - not found
implicitly[ExtCov[List[List[Int]]]] // fails - not found
implicitly[ExtCov[List[List[List[Int]]]]] // fails - not found
}
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