Question

所以我有这样的元组列表：

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)})

在这片土地上有很多快乐，但是当我像这样更改房间清单时：

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)})

我明白了：

[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)

所以看来这个列表现在是Object而不是之前的JField，为什么会这样？

Answer 1

如果您不从List

分离(，则此方法有效

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

基本上，它解析如下：

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

错误的发生是因为JObject构造函数需要JValue，但您传递的是fields，其类型为List.type。

scala列表类型不匹配

1 个答案: