Scala 的密封抽象与抽象类
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Scala's sealed abstract vs abstract class
提问by ?ukasz Lew
What is the difference between sealed abstractand abstractScala class?
sealed abstract和abstractScala类有什么区别？
回答by sepp2k
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.
区别在于密封类的所有子类（无论是否抽象）都必须与密封类在同一个文件中。
回答by Daniel C. Sobral
As answered, all directly inheritingsubclasses 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:
正如回答的那样，密封类（抽象或非抽象）的所有直接继承子类必须在同一个文件中。这样做的一个实际结果是，如果模式匹配不完整，编译器会发出警告。例如：
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 Treeis sealed, then the compiler warns unless that last line is uncommented.
如果Tree是sealed，则编译器会发出警告，除非最后一行未注释。
