在 Scala 中实现 ExpandoObject

Question

我正在尝试在 Scala 中实现 C#'s ExpandoObject-like 类。它应该是这样工作的：

val e = new ExpandoObject
e.name := "Rahul" // This inserts a new field `name` in the object.
println(e.name) // Accessing its value.

这是我迄今为止尝试过的：

implicit def enrichAny[A](underlying: A) = new EnrichedAny(underlying)
class EnrichedAny[A](underlying: A) {
  // ...
  def dyn = new Dyn(underlying.asInstanceOf[AnyRef])
}

class Dyn(x: AnyRef) extends Dynamic {
  def applyDynamic(message: String)(args: Any*) = {
    new Dyn(x.getClass.getMethod(message, 
      args.map(_.asInstanceOf[AnyRef].getClass) : _*).
      invoke(x, args.map(_.asInstanceOf[AnyRef]) : _*))
  }
  def typed[A] = x.asInstanceOf[A]
  override def toString = "Dynamic(" + x + ")"
}

class ExpandoObject extends Dynamic {
  private val fields = mutable.Map.empty[String, Dyn]
  def applyDynamic(message: String)(args: Any*): Dynamic = {
    fields get message match {
      case Some(v) => v
      case None => new Assigner(fields, message).dyn
    }
  }
}

class Assigner(fields: mutable.Map[String, Dyn], message: String) {
  def :=(value: Any): Unit = {
    fields += (message -> value.dyn)
  }
}

当我尝试编译这段代码时，我得到一个StackOverflowError。请帮我完成这项工作。 :) 谢谢。

Answer 1

玩了一会儿就搞定了。该解决方案虽然不是类型安全的（在这种情况下并不重要，因为这个小实用程序的目的是解决类型系统。:-)

trait ExpandoObject extends Dynamic with mutable.Map[String, Any] {
  lazy val fields = mutable.Map.empty[String, Any]
  def -=(k: String): this.type = { fields -= k; this }
  def +=(f: (String, Any)): this.type = { fields += f; this }
  def iterator = fields.iterator
  def get(k: String): Option[Any] = fields get k
  def applyDynamic(message: String)(args: Any*): Any = {
    this.getOrElse(message, new Assigner(this, message))
  }
}

implicit def anyToassigner(a: Any): Assigner = a match {
  case x: Assigner => x
  case _ => sys.error("Not an assigner.")
}

class Assigner(ob: ExpandoObject, message: String) {
  def :=(value: Any): Unit = ob += (message -> value)
}