[Scala] ImmutableList의 remove()

scala 2.9부터 List 객체의 remove 메소드가 사라졌다. Immutable 객체에 remove()가 어색했던 것 같다. 

http://www.scala-lang.org/files/archive/api/2.9.0/#scala.collection.immutable.List

2.8 버전에는 deprecated된 http://www.scala-lang.org/api/2.8.2/의 List의 remove 메소드를 확인할 수 있다.

defremove (p: (A) ⇒ Boolean) : List[A]

deprecated: 

1. use filterNot' instead

스칼라 2.11로 테스트 해보면 다음과 같다. 

scala> thrill.remove(s=>s.length ==4)

<console>:13: error: value remove is not a member of List[String]

       thrill.remove(s=>s.length ==4)

              ^

scala> thrill.filterNot(s=>s.length==4)

res13: List[String] = List(aa, bb)

scala> thrill.filterNot(s=>s.length==2)

res14: List[String] = List()

참고로 ListBuffer에는 remove()가 존재한다. Buffer는 문맥에 맞게 제공하고 있다. 

http://www.scala-lang.org/api/current/#scala.collection.mutable.ListBuffer

1. defremove(n: Int): A

   Removes the element on a given index position.

2. defremove(n: Int, count: Int): Unit

   

   Removes a given number of elements on a given index position.

1. def--=(xs: TraversableOnce[A]): ListBuffer.this.type

   Removes all elements produced by an iterator from this shrinkable collection.

2. def-=(elem: A): ListBuffer.this.type

   Remove a single element from this buffer.

3. def-=(elem1: A, elem2: A, elems: A*): ListBuffer.this.type

   Removes two or more elements from this shrinkable collection.

스칼라 2.11로 테스트 해보면 다음과 같다. 

scala> import scala.collection.mutable.ListBuffer

import scala.collection.mutable.ListBuffer

scala> var thrill = new ListBuffer[String]()

thrill: scala.collection.mutable.ListBuffer[String] = ListBuffer()

scala> thrill += "aaa"

res0: scala.collection.mutable.ListBuffer[String] = ListBuffer(aaa)

scala> thrill += "bbb"

res1: scala.collection.mutable.ListBuffer[String] = ListBuffer(aaa, bbb)

scala> thrill.filter(s => s.length == 2)

res4: scala.collection.mutable.ListBuffer[String] = ListBuffer()

scala> thrill.filter(s => s.length == 3)

res5: scala.collection.mutable.ListBuffer[String] = ListBuffer(aaa, bbb)

scala> thrill.remove(1)

res6: String = bbb

scala> thrill -= "bbb"

res7: scala.collection.mutable.ListBuffer[String] = ListBuffer(aaa)