implicit programming

Sample.scala

import java.util.Date
import org.joda.time.format.DateTimeFormat

// 暗黙のクラス

class Sample1 {

  def sample = {
    "Gunma".hello // => Hello, Gunma
  }

  implicit class HelloString(string: String) {

    def hello = {
      "Hello, " + string
    }

  }

}

// 暗黙の型変換

class Sample2 {

  def time(date: Date) = {
    date.getTime
  }

  def sample = {
    time(new Date())
    time("2015/07/18")
  }

  implicit def string2date(dateString: String): Date = {
    val formatter = DateTimeFormat.forPattern("yyyy/MM/dd")
    formatter.parseDateTime(dateString).toDate
  }

}

// 暗黙の引数

class Greet {

  def hello(implicit name: String) = {
    "Hello, " + name
  }

}

class Sample3 {

  implicit val name = "Gunma"

  def sample = {
    val greet = new Greet
    greet.hello("World") // => Hello, World
    greet.hello          // => Hello, Gunma
  }

}