用于案例类的Scala构造函数问题

Question

我对Scala中的某些东西感到困惑.我似乎有对象具有相同的地址,但内容不同.我在使用Kiama时遇到过这个问题.但为了简单起见,我把所有代码都煮到了这个:

object CaseTests {
  trait Attributable extends Product {
    var parent: Attributable = null;

    private def setChildConnections = {
        var i : Int = 0        
        for (i <- 0 until productArity) {
            productElement (i) match {
                case c : Attributable => c.parent = this
                case _ => 
            }
        }

    }
    setChildConnections
  }

  abstract class Tree extends Attributable { def id = super.toString }
    case class Pair (left : Tree, right : Tree) extends Tree { println(this+" = "+super.toString + " = ("+left.id+", "+right.id+")"); }
    case class Leaf (value : Int) extends Tree { println(this+" = "+super.toString); }

  def main(args: Array[String]): Unit = {
      val l1 = Leaf(1);
      val l2 = Leaf(1);
      val tree = Pair (Leaf (1), Pair (Leaf (1), Leaf (2)))
      val Pair(left1: Tree, sub: Tree) = tree
      val Pair(left2: Tree, right: Tree) = sub 
      println("left1 = "+left1.id)
      println("left2 = "+left2.id)
      println("left1.parent = "+left1.parent)
      println("left2.parent = "+left2.parent)
  }
}

当我运行我的测试用例时,我将其作为输出:

Leaf(1) = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
Leaf(1) = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
Leaf(1) = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
Leaf(1) = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
Leaf(2) = org.modelica.v4.tests.full.CaseTests$Leaf@de2f8005
Pair(Leaf(1),Leaf(2)) = org.modelica.v4.tests.full.CaseTests$Pair@d8e41584 = (org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2, org.modelica.v4.tests.full.CaseTests$Leaf@de2f8005)
Pair(Leaf(1),Pair(Leaf(1),Leaf(2))) = org.modelica.v4.tests.full.CaseTests$Pair@6a311526 = (org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2, org.modelica.v4.tests.full.CaseTests$Pair@d8e41584)
left1 = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
left2 = org.modelica.v4.tests.full.CaseTests$Leaf@fe67d8d2
left1.parent = Pair(Leaf(1),Pair(Leaf(1),Leaf(2)))
left2.parent = Pair(Leaf(1),Leaf(2))

我不明白(我怀疑这是因为我遗漏了一些关于Scala/Java等价的细微观点,或者我只是误解了输出)是left1和left2看起来有相同的地址(或者我是误解了,但不同的父母？!

如果有人能让我直截了当,我会非常感激.谢谢.

PS - 我正在运行Scala 2.9,以防万一.

Answer 1

left1并且left2不是同一个对象.试试println(left1 eq left2),它会打印错误.默认toString方法调用Integer.toHexString(hashCode),因此id如果两个对象的哈希码匹配,则必须获得相同的结果.它确实如此,因为案例类自动得到了体面hashCode和equals实现.