mutable.ArrayBuffer vs immutable.Vector

gistfile1.scala

import scala.collection._
import com.twitter.util._

scala> val buffer = mutable.ArrayBuffer.empty[Int]
scala> println(Time.measure { (0 to 50000000).foreach { buffer += _ } }.inMillis)
17610

scala> var vector = immutable.Vector.empty[Int]
scala> println(Time.measure { (0 to 50000000).foreach { vector :+= _ } }.inMillis)
7865

// do it again, just in case
scala> val buffer = mutable.ArrayBuffer.empty[Int]
scala> println(Time.measure { (0 to 50000000).foreach { buffer += _ } }.inMillis)
24742

// let's try a java.util.ArrayList
val buffer2 = new java.util.ArrayList[Int]
scala> println(Time.measure { (0 to 50000000).foreach { buffer2.add(_) } }.inMillis)
7923