Why am I getting 0-length ArrayBuffers?

ArrayBuffer's constructor takes one argument--the length of the internal buffer that will initially be used to store the data.  It doesn't actually put anything in the buffer.

However, the companion object apply method takes anything you pass to it and makes an ArrayBuffer containing that.

So:

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> ArrayBuffer(3)  // This is the apply method on the companion
res0: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(3)

scala> new ArrayBuffer[Int](3) { def seeInside = array }
res1: scala.collection.mutable.ArrayBuffer[Int]{def seeInside: Array[AnyRef]} = ArrayBuffer()

scala> res1.seeInside
res2: Array[AnyRef] = Array(null, null, null)

  --Rex



On Thu, May 12, 2011 at 9:12 PM, Ken McDonald <ykkenmcd@gmail.com> wrote:

scala> import scala.collection.mutable.ArrayBufferimport scala.collection.mutable.ArrayBuffer
scala> new ArrayBuffer[Int](3)res1: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
scala> res1res2: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
scala> res1.lengthres3: Int = 0
This does not work at all like I would have thought reading the documentation.