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Consider the following code: object foo { trait Bar[Q[_]] implicit object OptionBar extends Bar[Option] def test[T, C[_]](c: C[T])(implicit bar: Bar[C]) = () def main(args: Array[String]) { test(Some(42): Option[Int]) //??? } } This works, but I need to type the Some(42) as Option[Int], else the implicit object OptionBar won't be resolved (because a Bar[Some] is expected instead). Is there a way to avoid the explicit typing, so that I get the implicit OptionBar object in test even if I feed test with a Some or None? [Clarification] I used Option here just as example, it should also work if I have a Bar for an abstract class etc. The solution should also work when other, unrelated Bars are in scope, say implicit object listBar extends Bar[list] [Update] It seems that making Bar's parameter contravariant does the trick: object foo { trait Bar[-Q[_]] //<--------------- implicit object OptionBar extends Bar[Option] implicit object ListBar extends Bar[List] def test[T, C[_]](c: C[T])(implicit bar: Bar[C]) = () def main(args:Array[String]) { test(Some(42)) } } But of course this is a severe limitation of the possibilities in Bar, so I still hope for a better answer.

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