What does ":" means in method type in scala?

Question

Here is the method signature example:

someMethod [A <: BaseType : SecondType : ClassTag] trait BaseType {} trait SecondType[A] {}

ClassTag is scala.reflect.ClassTag

What does ":" means?

Does BaseType influence to SecondType or/and ClassTag parametrization?

For me when I see [A <: BaseType] I understand that I should call someMethod with type parameter that implements/extends trait BaseType, but what other parameters are used for?

possible duplicate of What are Scala context and view bounds? — 4e6
– 4e6, Commented Sep 12, 2014 at 5:27
There are only examples like (A:a, B,b), not likle (A:a:b:c). — Cherry
– Cherry, Commented Sep 12, 2014 at 5:31
Why are there questions about "what are all the uses of underscore" but not "what are all the uses of colon?" or "dot?" or "dollar?" — som-snytt
– som-snytt, Commented Sep 12, 2014 at 5:43

som-snytt · Accepted Answer · 2014-09-12 05:40:58Z

That's probably obvious to someone, but:

scala> trait X[A] ; trait Y[A] scala> def f[A : X : Y] = 42

yields

 def f[A](implicit evidence$1: X[A], evidence$2: Y[A]) = 42

under -Xprint:parser. So it wants both X[A] and Y[A].

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