why does filter have to be defined for pattern matching in a for loop in scala?

Question

To create a new class that can be used in a Scala for comprehension, it seems that all you have to do is define a map function:

scala> class C[T](items: T         


        

Answer 1

See the difference:

scala> for ((k, v) <- List(1 -> 2, 3 -> 4, 5)) yield k -> v
res22: List[(Any, Any)] = List((1,2), (3,4))

scala> List(1 -> 2, 3 -> 4, 5).map{case (k, v) => k -> v}
scala.MatchError: 5