Scala lazy的应用，流Stream和视图View

object StreamDemo {

  //生成流的方法
  def numStream(n: BigInt): Stream[BigInt] = n #:: numStream(n + 1)

  def main(args: Array[String]): Unit = {
    val stream = numStream(1)

    //初始只有一个元素
    println(stream) //Stream(1, ?)

    //获取第一个元素
    println(s"head = ${stream.head}") //head = 1

    //获取尾部
    println(s"tail = ${stream.tail}") //tail = Stream(2, ?)

    //调用tail方法之后，动态产生了元素2
    println(stream) //Stream(1, 2, ?)

    //为什么不是Stream(2, 4, ?)
    println(stream.map(_ * 2))  //Stream(2, ?)
  }
}

def main(args: Array[String]): Unit = {

  val seq: immutable.Seq[Int] = (1 to 100).filter(n => n.toString.equals(n.toString.reverse))
  println(seq)  //Vector(1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99)

  //调用结果view之前，并不会去执行filter等操作
  val view: SeqView[Int, immutable.IndexedSeq[Int]] = (1 to 100).view.filter(n => n.toString.equals(n.toString.reverse))
  println(view) //SeqViewF(...)

}