Partial函数的定义

scala> val isVeryTasty: PartialFunction[String, String] = { case "Glazed Donut" | "Strawberry Donut" => "Very Tasty"}
isVeryTasty: PartialFunction[String,String] = <function1>

scala> isVeryTasty("Glazed Donut")
res3: String = Very Tasty

 

Partianl函数的组合使用：

 

code :

 

  println("\nStep 1: How to define a Partial Function named isVeryTasty")
  val isVeryTasty: PartialFunction[String, String] = { case "Glazed Donut" | "Strawberry Donut" => "Very Tasty"}



  println("\nStep 2: How to call the Partial Function named isVeryTasty")
  println(s"Calling partial function isVeryTasty = ${isVeryTasty("Glazed Donut")}")
  // NOTE: you will get scala.MatchError



  println("\nStep 3: How to define PartialFunction named isTasty and unknownTaste")
  val isTasty: PartialFunction[String, String] = {
    case "Plain Donut" => "Tasty"
  }

  val unknownTaste: PartialFunction[String, String] = {
    case donut @ _ => s"Unknown taste for donut = $donut"
  }



  println("\nStep 4: How to compose PartialFunction using orElse")
  val donutTaste = isVeryTasty orElse isTasty orElse unknownTaste
  println(donutTaste("Glazed Donut"))
  println(donutTaste("Plain Donut"))
  println(donutTaste("Chocolate Donut"))

result:

Step 1: How to define a Partial Function named isVeryTasty

Step 2: How to call the Partial Function named isVeryTasty
Calling partial function isVeryTasty = Very Tasty

Step 3: How to define PartialFunction named isTasty and unknownTaste

Step 4: How to compose PartialFunction using orElse
Very Tasty
Tasty
Unknown taste for donut = Chocolate Donut