斯卡拉列表类型不匹配

Question

所以我有过这样的元组的列表：

val rooms = List(("Hi", "mom"),("hi", "dad")) 
val foo = rooms.map(arg =>{ 
        var fields = List 
        (new JField("greeting",arg._1), 
         new JField("recipient",arg._2)) 
         new JObject(fields)}) 

了。在土地多的快乐，但是当我改变了房间列表，像这样：

case class Room(greeting:String, recipient:String) 
val rooms = List(Room("Hi", "mom"),Room("hi", "dad")) 
val foo = rooms.map(arg =>{ 
        var fields = List 
        (new JField("greeting",arg.greeting), 
         new JField("recipient",arg.recipient)) 
         new JObject(fields)}) 

我得到：

[error] <file>: type mismatch; 
[error] found : scala.collection.immutable.List.type (with underlying type object List) 
[error] required: List[blueeyes.json.JsonAST.JValue] 
[error]      new JArray(fields) 

因此，看起来该列表现在是对象而不是以前的JField，为什么？

Answer 1

，如果你不分离从(的List它的工作原理：

var fields = List(
    new JField("greeting", arg.greeting), 
    new JField("recipient", arg.recipient)) 

基本上，它的解析如下：

var fields = List       // assign the List companion object 

(new JField("greeting", arg.greeting), // construct a tuple with two items 
    new JField("recipient", arg.recipient)) // ...but don't use or assign it 

new JObject(fields)      // Make JObject containing the type 

的错误出现，因为JObject构造函数需要一个JValue但你通过它fields其类型List.type。