scala 隐式参数

scala implicit 提供隐式转换和隐式变量两种功能

隐式转换，scala 对象由一种类型，隐式地转换成另外一种类型，如下：

package com.st.base

object Main {
  def main(args: Array[String]): Unit = {
    class Human{def speek(){println("human can speek")};};

    // 下面两种方式，都可以让 Human 对象隐式转为 Monkey 对象
    implicit class Monkey(human: Human){def sound(){println("monkey can't speek!")}};
    implicit def converseToMonkey(human: Human): Monkey = {
      return new Monkey;
    }

    var human = new Human;
    human.speek();
    human.sound();  // Human 对象被隐式转换为 Monkey 对象
  }
}

输出：
human can speek
monkey can't speek!

隐式变量，包括普通变量和参变量

package com.st.base

object Main {

def main(args: Array[String]): Unit = {
  // 定义隐式变量
  implicit val name: String = "lili";

  // name 隐式参数，way 默认值 bus，num 默认值 3
  def goToSchool(implicit name: String, way: String = "bus", num: Int = 3): Unit ={
    println(name + " go to school by " + way + " " + String.valueOf(num));
  }

  // name="lili"，way= "lili", num = 3，隐式参数覆盖默认值
  goToSchool;

  // name = "xiaoming", way = "bus", num  = 3, 实参覆盖隐式参数和默认值
  goToSchool("xiaoming", "bike") 
}

 } 

输出：
lili go to school by lili 3
xiaoming go to school by bike 3