What is the difference between sealed abstract
and abstract
Scala class?
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问题:
回答1:
The difference is that all subclasses of a sealed class (whether it's abstract or not) must be in the same file as the sealed class.
回答2:
As answered, all directly inheriting subclasses of a sealed class (abstract or not) must be in the same file. A practical consequence of this is that the compiler can warn if the pattern match is incomplete. For instance:
sealed abstract class Tree
case class Node(left: Tree, right: Tree) extends Tree
case class Leaf[T](value: T) extends Tree
case object Empty extends Tree
def dps(t: Tree): Unit = t match {
case Node(left, right) => dps(left); dps(right)
case Leaf(x) => println("Leaf "+x)
// case Empty => println("Empty") // Compiler warns here
}
If the Tree
is sealed
, then the compiler warns unless that last line is uncommented.