scala 偏函数

Posted 2021-01-03 jason-dong

package com.jason.qianfeng

object PartialFuncTest {
  def div: PartialFunction[Int, Int] = {
    case i if i != 0 => 100 / i
  }

  def r1: PartialFunction[Int, String] = {
    case 1 => "one"
    case 2 => "two"
    case _ => "other"
  }

  def r2: PartialFunction[Int, String] = {
    case 1 => "one"
  }

  def r3: PartialFunction[Int, String] = {
    case 2 => "two"
  }

  def r4: PartialFunction[Int, String] = {
    case _ => "other"
  }

  def r6: PartialFunction[String, String] = {
    case "one" => "haha one"
    case "two" => "wawo two"
  }

  def main(args: Array[String]): Unit = {
    val s = "=" * 10
    println(s"$s test function div $s")
    println(s"div.isDefinedAt(0):" + div.isDefinedAt(0))
    println(s"div.isDefinedAt(1):" + div.isDefinedAt(1))
    println(s"div(2) = " + div(2))

    println(s"$s test function r1 $s")
    println(s"r1(2) = " + r1(2))

    println(s"$s orElse $s")
    val r5 = r2 orElse r3 orElse r4
    println(s"r5(2) = " + r5(2))

    println(s"$s  andThen $s")
    val r7: PartialFunction[Int, String] = r1 andThen r6
    println(s"r7(1) = " + r7(1))
  }
}

执行结果

========== test function div ==========
div.isDefinedAt(0):false
div.isDefinedAt(1):true
div(2) = 50
========== test function r1 ==========
r1(2) = two
========== orElse ==========
r5(2) = two
==========  andThen ==========
r7(1) = haha one

总结

1.什么是偏函数：例如上述的函数div，传入的参数为 int，反汉之也是int，但是函数并不是对所有输入的int都进行处理，而是只处理不为0 的int

2.orElse 方法可以拼接多个偏函数，类似if...else

3.andThen 方法是把多个偏函数串联起来，第一个函数的结果作为参数传给第二个，以此类推