Scala Equality和HashCode

深度Scala在mutability和上呈现此代码equality.

class Point2(var x: Int, var y: Int) extends Equals {
def move(mx: Int, my: Int) : Unit = {
  x = x + mx
  y = y + my
}
override def hashCode(): Int = y + (31*x)

def canEqual(that: Any): Boolean = that match {
  case p: Point2 => true
  case _ => false
}
override def equals(that: Any): Boolean = {
def strictEquals(other: Point2) =
  this.x == other.x && this.y == other.y
  that match {
    case a: AnyRef if this eq a => true
    case p: Point2 => (p canEqual this) && strictEquals(p)
     case _ => false
  }
}
}

然后,它执行评估.

scala> val x = new Point2(1,1)
x: Point2 = Point2@20
scala> val y = new Point2(1,2)
y: Point2 = Point2@21
scala> val z = new Point2(1,1)
z: Point2 = Point2@20

接下来,HashMap创建一个.

scala> val map = HashMap(x -> "HAI", y -> "WORLD")
map: scala.collection.immutable.HashMap[Point2,java.lang.String] =
Map((Point2@21,WORLD), (Point2@20,HAI))

scala> x.move(1,1)

scala> map(y)
res9: java.lang.String = WORLD

据我所知,自从发生变异后map(x)将会返回.由于突变,重新计算了hashCode .结果,当检查是否在,没有地图的匹配是新的.NoSuchElementExceptionxxx.move(1,1xmaphashCodexhashCode

scala> map(x)
java.util.NoSuchElementException: key not found: Point2@40
...

由于zequals(value)最初插入x的HashMap,以及hashCode为什么抛出异常？

scala> map(z)
java.util.NoSuchElementException: key not found: Point2@20

编辑在我看来,这个例子显示了命令式编程的复杂性(坏).