scala - 案例类 toString 与 Iterable 特性纠缠在一起？

Question

似乎当一个案例类扩展 Iterable[T] , toString方法变了。

case class MyPoint(x: Int, y: Int)

case class MyOtherPoint(x: Int, y: Int) extends Iterable[Double] {
  def iterator: Iterator[Double] = Iterator.fill(4)(1.0)
}

object Main extends App {
  val my_pt = MyPoint(4,5)
  println(my_pt) // MyPoint(4,5)
  // println(my_pt.iterator) // ERROR, iterator is not a member of MyPoint
  val my_other_pt = MyOtherPoint(4, 5)
  println(my_other_pt) // MyOtherPoint(1.0, 1.0, 1.0, 1.0)
  println(my_other_pt.productIterator.toList) // List(4, 5)
}

这似乎很不幸，特别是考虑到虽然 case 类扩展了 Product默认情况下，因此有 productIterator ，他们不应该扩展 Iterable .

这是 Scala 编译器中的错误吗？

Answer 1

Is this a bug in the Scala compiler?

不，这是规范中定义的行为( section §5.3.2 ，重点是我的):

Every case class implicitly overrides some method definitions of class scala.AnyRef unless a definition of the same method is already given in the case class itself or a concrete definition of the same method is given in some base class of the case class different from AnyRef. In particular:

• Method toString: String returns a string representation which contains the name of the class and its elements.

你看到的是 Iterable的结果继承 TraversableLike ，其中有以下 toString覆盖:

override def toString = mkString(stringPrefix + "(", ", ", ")")

此外，如果您在 Xprint:jvm 下编译可以看到 MyOtherPoint继承的很多方法，包括覆盖 toString :

case class MyOtherPoint extends Object with Iterable with Product with Serializable {
  // removed all other methods for brevity
  override def toString(): String = MyOtherPoint.super.toString();
}