Present a 64-bit long Int in a URI-safe Base 64 encoding, in scala

UriBase64Long.scala

/*
Usage:
> UriBase64Long(1234567891011L).mkString
val res41: String = dqTp5Kaa

> Range(0,8).map(_=>Random.nextLong()).flatMap(UriBase64Long(_)).mkString
val res42: String = 6MO_7T1drnVveBdcHYG08PcCDyx5QlyU@~T8UpTr6Go02cjd7@IJBYSHk0EttfhS

*/

class UriBase64Long(start:Long) extends Iterator[Char] {
    import UriBase64Long._
    var remainder = start
    var nextsLeft = UriBase64Long.itrCount
    override def hasNext = (nextsLeft!=0)
    override def next():Char = {
        val thisChar = remainder & UriBase64Long.bitMask
        remainder = remainder >>> 7
        nextsLeft = nextsLeft - 1;
        UriBase64Long.dict(thisChar.toInt)
    }
}

object UriBase64Long {
    val dict = Seq( 'a'->'z', 'A'->'Z', '0'->'9').flatMap( p => Range(p._1, p._2) ).map(_.toChar).mkString + "-~_@$"
    val dictSize = dict.size
    private val bitMask = 63 // 7 bits
    private val itrCount = 64/8 // Long is a 64-bit integer

    def apply( aLong:Long ) = new UriBase64Long(aLong)
}