Question

我有一个带有两个输入的simpleNode类，你只能填充其中一个，这些都是Scala中的Map，但我必须检查地图中的数据类型才能填充任何输入

我写的代码是：

class SimpleNode (
  val uriTriples: collection.mutable.Map[String, List[String]] = collection.mutable.Map.empty,
  val valueTriples: collection.mutable.Map[String, Map[String,String]] = collection.mutable.Map.empty
                ) 
  {              
    def this(map:collection.mutable.Map) = {
      map.values.head match {
      case uri : List[String] => this(uris,null) 
      case values : Map[String,String] => this(null,values)
      case _=>
    }
  }
}

我总是面对错误：

a:34: error: 'this' expected but identifier found.
[INFO]        map.values.head match {
[INFO]        ^

Answer 1

消除歧义的常用策略：

class SimpleNode (
  val uriTriples: collection.mutable.Map[String, List[String]] = collection.mutable.Map.empty,
  val valueTriples: collection.mutable.Map[String, Map[String,String]] = collection.mutable.Map.empty
)
  {
    def this(map:mutable.Map[String, List[String]]) = this(map, null)
    def this(map:mutable.Map[String, Map[String,String]])(implicit d: DummyImplicit) = this(null, map)
}

或者工厂更加行人：

object SimpleNode {
  def apply(...) = ???
}

基于scala中的条件重载构造函数

1 个答案: