克隆ListBuffer一成不变的问题斯卡拉

Question

我ListBuffer[ListBuffer[Int]]型var x在我使用的功能clone克隆和设置到另一个var y，然后我用这个新var y功能update来更新内容，但是当我检查var x的原始内容与var y相同吗？为什么是这样？我究竟做错了什么？他们是一种解决方法吗？我试图实现ListBuffer的副本，我可以在不更改初始ListBuffer的原始内容的情况下进行修改。

Answer 1

clone不仅使浅拷贝，你需要深拷贝：

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))