scala - Scala追加到可变的LinkedList

Question

请检查一下

import scala.collection.mutable.LinkedList

var l = new LinkedList[String]

l append LinkedList("abc", "asd")

println(l)
// prints 
// LinkedList()

但

import scala.collection.mutable.LinkedList

var l = new LinkedList[String]

l = LinkedList("x")
l append LinkedList("abc", "asd")

println(l)
// prints 
// LinkedList(x, abc, asd)

为什么第二个代码段有效但第一个无效？这是在Scala 2.10上

Answer 1

该文档说If this is empty then it does nothing and returns that. Otherwise, appends that to this.。就是您所观察到的。如果您确实需要可变列表，建议您改用scala.collection.mutable.ListBuffer，它可以

val lb = new ListBuffer[Int]

scala> lb += 1
res14: lb.type = ListBuffer(1)

scala> lb
res15: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1)

scala> lb ++= Seq(1,2,3)
res17: lb.type = ListBuffer(1, 1, 2, 3, 1, 2, 3)

scala> lb
res18: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 1, 2, 3, 1, 2, 3)