Scala mutable.LinkedHashMap：for 循环移除奇怪的行为

Question

我有一个 mutable.LinkedHashMap 并尝试在 for 循环中删除项目。但是，如果发生删除，for 循环也会停止。

scala> val a = mutable.LinkedHashMap[Int, Int](1->1, 2->2, 3->3)
# when no remove occurs, for-loop works as expected
scala> for( (k,v) <- a ) { println(k);  }
1
2
3
# following code doesn't work, only remove 1 and stop
scala> for( (k,v) <- a ) { println(k); a.remove(k) }
1
# following code work as expected
scala> a.keys.foreach{ k => println(k); a.remove(k) }
1
2
3

我很好奇为什么要删除 stop for-loop。

Answer 1

"remove on iteration" 在“2.13.0-M5”中工作正常，但在早期版本中不工作。但还是不建议砍掉你所在的树枝

见2.13例子： https://scastie.scala-lang.org/prayagupd/Cq2wUKP3TtmaL5IDMVKRfw/7

import scala.collection.mutable

val data = mutable.LinkedHashMap[Int, Int](1 -> 1, 2 -> 2, 3 -> 3)

println("before: " + data)

for ((k, v) <- data) {
  println("removing key: " + k + " from map " + data)
  data.remove(k)
}

println("after: " + data)

输出：

before: LinkedHashMap(1 -> 1, 2 -> 2, 3 -> 3)
removing key: 1 from map LinkedHashMap(1 -> 1, 2 -> 2, 3 -> 3)
removing key: 2 from map LinkedHashMap(2 -> 2, 3 -> 3)
removing key: 3 from map LinkedHashMap(3 -> 3)
after: LinkedHashMap()

Scala mutable.LinkedHashMap：for 循环移除奇怪的行为

Scala mutable.LinkedHashMap: for-loop remove strange behavior

scala

linkedhashmap