任何精通
Scala的人都可以解释为什么这样有效：
scala> Tuple2[String,String]("w3wre","werffd")
res0: (String,String) = (w3wre,werffd)
scala> val (s1:Any,s2:Any) = Tuple2[String,"werffd")
s1: Any = w3wre
s2: Any = werffd
但不是吗？
scala> Tuple2[String,null)
res1: (String,null)
scala> val (s1:Any,null)
scala.MatchError: (w3wre,null) (of class scala.Tuple2)
at .<init>(<console>:9)
at .<clinit>(<console>)
...
(显然Any-type可以包含空值：
scala> val n:Any = null n: Any = null scala> val n:Any = null.asInstanceOf[String] n: Any = null
)
？
解决方法
语言规范明确指出这种类型模式不匹配null(
8.2 Type Patterns,强调我的)：
Type patterns consist of types,type variables,and wildcards. A type pattern T is of one of the following forms:
- A reference to a class C,p.C,or T#C. This type pattern matches any non-null instance of the given class.
但是,我不知道语言设计者在不匹配null背后的推理.
