Ask for an example showing how immutability contributes to Scala's concurrency mechanism
===

The following example shows that one can use a mutable variable as message sended to an **Actor**. So why people say that immutability is the reason why Scala is good for concurrency?

    import scala.io._
    import scala.actors._
    import Actor._
    
    def getPageSize(url : String) = Source.fromURL(url).mkString.length
    
    var abc = "http://www.verycd.com"
    
    def getPageSizeConcurrently() = {
      abc = "http://www.twitter.com"  // changing value
      
      val caller = self
      actor { caller ! (abc, getPageSize(abc)) }
      receive {
        case (url, size) =>
          println("Size for " + url + ": " + size)            
      }
    }

    getPageSizeConcurrently