scala学习笔记（十五） 高等类型

类或特质可以定义一个在子类中被具体化的抽象类型，如下：
 trait Reader {
    type Contents //这里定义一个抽象类型，子类中必须指定这个类型
    def read(fileName: String): Contents
  }
 
  class StringReader extends Reader {
    type Contents = String
    def read(fileName: String) =Source.fromFile(fileName, "UTF-8").mkString
  }
 
  class ImageReader extends Reader {
    type Contents = BufferedImage
    def read(fileName: String) =ImageIO.read(new File(fileName))
  }
 
  //上面的抽象类型也可以写为下面的这种形式 
这种方式是 类型参数
  trait ReaderC[C] {
    def read(fileName: String): C
  }
 
抽象类型还可以使用界定，与类型参数一样
trait Listener {
    type Event <: java.util.EventObject
  }
这样在子类中指定的时候EVENT必须是EventObject的一个兼容的类型
 
 
package demo
 
/**
 * @author Administrator
 */
object ScalaType {
 
  object show
  object then
  object around
 
  def main(args: Array[String]): Unit = {
    //   val bug = new Bug()
    //   bug move 4 and show and then move 6 and show turn around move 5 and show
 
    printValues((x: Int) => x * x, 3, 6)
    printValues(Array(1, 1, 2, 3, 5, 8, 13, 21,34, 55), 3, 6)
  }
 
  class Bug {
    var direction: Boolean = true
    var postion: Int = 0
    def move(step: Int) = {
      val tmp = if (direction) step else -step
      postion += tmp
      this
    }
 
    def turn(): this.type = {
      direction = !direction
      this
    }
 
    //   def show = {
    //     print(postion + " ")
    //     this
    //   }
 
    def and(obj: show.type) = { print(postion +" "); this }
    def and(obj: then.type) = this
    def turn(obj: around.type): this.type =turn()
  }
 
  def fun(obj: { def close(): Unit }, f: { defclose(): Unit } => Unit) {
    try {
      f(obj)
    } catch {
      case e: Exception => obj.close();e.printStackTrace()
    } finally {
      obj.close()
    }
  }
 
  def printValues(f: { def apply(v: Int): Int}, from: Int, to: Int) {
    for (i <- from to to)println(f.apply(i))
  }
 
  abstract class Dim[T](val value: Double, valname: String) {
    this: T
4000
=>
    protected def create(v: Double): T
    def +(other: Dim[T]) = create(value +other.value)
    override def toString() = value + "" + name
  }
 
  class Seconds(v: Double) extendsDim[Seconds](v, "s") {
    override def create(v: Double) = newSeconds(v)
  }
 
  class Meters(v: Double) extendsDim[Meters](v, "m") {
    override def create(v: Double) = newMeters(v)
  }
 
}