Using case classes to filter matching cases in Scala

abstract class A0
 
case class A() extends A0
 
case class B() extends A0
 
case class C() extends A0
 
val list = List( A(), A(), B(), C(), C(), C() )
 
val len1 = list filter ( _  match {case A() => true; case _ => false} ) length

val len2 = list filter ( _  match {case _:A => true; case _ => false} ) length

val len3 = list filter ( x => x match {case A() => true; case _ => false} ) length

printf("=> len1: %d, len2: %d, len3: %d \n",len1,len2,len3)