lazy-exprs.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 96 行

object TestExpressions {

  def patmatchScrut {
    lazy val z1: Option[String] = { println("forced <z1>"); Some("lazy z1") }
    
    val res = z1 match {
      case Some(msg) => msg
      case None => "failed"
    }
    print("lazy val in scrutinee: ")
    if (res == "lazy z1")
      println("ok")
    else
      println("failed")
  }

  def patmatchCase {
    val t: Option[String] = Some("test")
    val res = t match {
      case Some(msg) => 
        lazy val z1 = { println("forced <z1>"); "lazy z1" }
        z1
    
      case None => "failed"
    }
    print("lazy val in case: ")
    if (res == "lazy z1")
      println("ok")
    else
      println("failed")
  }


  def patmatchPat {
    lazy val Z1 = { println("forced <z1>"); "lazy Z1" }
    print("lazy val in case: ")
    val t: Option[String] = Some("lazy Z1")
    t match {
      case Some(Z1) => 
        println("ok")
    
      case None =>
        println("failed")
    }
  }

  def ifcond {
    lazy val z1 = { println("forced <z1>"); "lazy z1" }
    print("lazy val in if condition: ")
    if (z1 == "lazy z1")
      println("ok")
    else
      println("failed")
  }


  lazy val LazyField = { println("forced LazyField"); "LazyField" }

  def testPatMatchField {
    print("lazy val in pattern: ")
    val t: Option[String] = Some("LazyField")
    t match {
      case Some(LazyField) => 
        println("ok")
    
      case None =>
        println("failed")
    }
  }    

  lazy val (x, y) = ({print("x"); "x"}, {print("y"); "y"})
  def testPatLazyVal {
    println("lazy val with patterns:")
    print("x and y: ")
    println("(" + x + ", " + y + ")")
    lazy val (x1, y1) = ({print("x1"); "x1"}, {print("y1"); "y1"})
    print("x1 and y1: ")
    println("(" + x1 + ", " + y1 + ")")
  }

  def test {
    patmatchScrut
    patmatchCase
    patmatchPat
    ifcond
    testPatMatchField
    testPatLazyVal
  }
}


object Test extends Application {

  TestExpressions.test
}