类型类的scala存在类型

Question

I want to define a function like this

def showList(items: Seq[_ : Show]) = {...} type parameter of Seq is any type that has an context bound Show

Thus I could call showList(Seq(1, "abc")) .

How should declare the method ?

Answer 1

def showList[A: Show](items: Seq[A]) = { ... }

or more explicitly (with the advantage of having the type class instance directly available)

def showList[A](items: Seq[A])(implicit ev: Show[A]) = { ... }

For the specific case, since scala collections are monomorphic, you'll need a Show[Any] instance.