Question

I created an abstract base class as follows:

abstract class parent

Then I went ahead and created two case classes inheriting from the parent class:

case class child1(name:String,category:String) extends parent

case class child2(name:String,category1:String,category2:String) extends parent

Then for kicks I created a list of type parent and appended child1 and child2 to it:

val childList = List[parent]()

scala> child1("Child","One") :: child2("Child","Two","dhshs")::childList
res2: List[parent] = List(child1(Child,One), child2(Child,Two,dhshs))

So far so good, the List[Parent] has the two child types in it.

Now, I want to traverse the List and based on the underlying type of the child, do something special for that particular type. So I do this:

scala> res2 map {case child1 => "Child1";case child2 => "Child2"}

I expected to see a List[String]("Child1","Child2"), instead I got the following:

<console>:15: error: unreachable code
              res2 map {case child1 => "Child1";case child2 => "Child2"}

Now for some more kicks, I did the following:

scala> res2 map {r => r match {case child1 => "Child1"}}
res8: List[java.lang.String] = List(Child1, Child1)

scala> res2 map {case child1 => "Child1"}
res9: List[java.lang.String] = List(Child1, Child1)

As you can see, I got “Child1” as my List entry, even for “child2” I get a Child1.

Pretty confused, can somebody tell me whats going on here?

Answer 1

The problem is here: child1 and child2 are new variables created to house the result.

res2 map {case child1 => "Child1";case child2 => "Child2"}

try this:

res2 map {case x:child1 => "Child1";case y:child2 => "Child2"}

x and y are the variables with the associated types child1 and child2 respectively.