or is it the "typeclass trick" using implicits
No, I don't see any relevance to typeclasses and implicits here
Monoid[T]with anything that has a type parameter and explicit instances, and your question remains the same
Monoid[Int], you know that the Monoid is for Int
State, but you don't know which State
Modelwithout knowing its
State, you could do that with universal types too no?
_you are using there doesn't mean what you think it means
def f[Model[_]] = ???
def f(model: Model[_]) = ???