scala - 克隆 ListBuffer 不可变问题 Scala

Question

我有一个 var x类型 ListBuffer[ListBuffer[Int]]我在其中使用函数 clone 进行克隆并设置为另一个 var y , 然后我使用函数 update在这个新 var y更新内容，但是当我查看 var x 的原始内容时同var y ?为什么是这样？我究竟做错了什么？他们是一种解决方法吗？我正在尝试获得一份 ListBuffer 的副本，我可以在不更改初始 ListBuffer 的原始内容的情况下对其进行修改。

Answer 1

clone只做一个浅拷贝，你需要一个深拷贝:

scala> import collection.mutable.ListBuffer
import collection.mutable.ListBuffer

scala> var a = ListBuffer(ListBuffer(1, 2), ListBuffer(3,4))
a: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(1, 2), ListBuffer(3, 4))


scala> var b = a.clone
b: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(1, 2), ListBuffer(3, 4))

scala> b(0)(0) = 100

scala> a
res1: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(100, 2), ListBuffer(3, 4))

scala> b
res2: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(100, 2), ListBuffer(3, 4))

scala> var c = a.clone.map(_.clone)
c: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(100, 2), ListBuffer(3, 4))

scala> c(0)(0) = 1000

scala> c
res3: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(1000, 2), ListBuffer(3, 4))

scala> a
res4: scala.collection.mutable.ListBuffer[scala.collection.mutable.ListBuffer[Int]] = ListBuffer(ListBuffer(100, 2), ListBuffer(3, 4))