O(n) size by default... great.

gistfile1.scala

def time[R](block: => R): R = {
    val t0 = System.currentTimeMillis
    val result = block    // call-by-name
    val t1 = System.currentTimeMillis
    println("Elapsed time: " + (t1 - t0) + "ms")
    result
}

val list1 = 1 to 10000 toList
val ary1 = 1 to 10000 toArray

time { (1 to 1000000).foreach { _ => list1.size } } // Elapsed time: 22672ms
time { (1 to 1000000).foreach { _ => ary1.size } } // Elapsed time: 20ms