非詳盡的比賽

Question

爲什麼不下面產生警告，失蹤警告時-unchecked啓用：

object Order { 
    sealed trait EntryOption 
    case object EmptyEntry extends EntryOption 
    trait Entry extends EntryOption 

    def isEmpty(a: EntryOption): Boolean = a match { 
     case EmptyEntry => true 
// case _: Entry => false 
    } 
} 

看來我有完全相同的斯卡拉2.8.0的日子same problem before，沒有足夠的答案。

---

編輯

@Jed它不會對我意義的警告只發出一個非抽象類Entry。考慮以下情況：

trait Order { 
    sealed trait EntryOption 
    case object EmptyEntry extends EntryOption 
    abstract sealed class Entry extends EntryOption 

    def isEmpty(a: EntryOption): Boolean = a match { 
    case EmptyEntry => true 
// case _: Entry => false 
    } 
} 

trait OrderImpl extends Order { 
    final class EntryImpl extends Entry 
} 

只有這樣，才能使警告顯示是有一個具體的類OrderEntry！

Answer 1

它在主幹上抱怨：

scala> object Order { 
    | sealed trait EntryOption 
    | case object EmptyEntry extends EntryOption 
    | trait Entry extends EntryOption 
    | 
    | def isEmpty(a: EntryOption) : Boolean = a match { 
    |  case EmptyEntry => true 
    | // case _: Entry => false 
    | } 
    | } 
<console>:18: warning: match is not exhaustive! 
missing combination   Entry 

      def isEmpty(a: EntryOption) : Boolean = a match { 
                ^
defined module Order 

Answer 2

條目是一個特質，而不是案例類。