التفكيك

ما التفكيك؟

تفكيك Tuple

object Main {
  def main(args: Array[String]): Unit = {
    val pair = ("Ada", 1815)
    val (name, year) = pair
    println(s"$name was born in $year")
  }
}

Tuples في match

object Main {
  def quadrant(p: (Int, Int)): String = p match {
    case (0, 0) => "origin"
    case (x, 0) => s"on x-axis at $x"
    case (0, y) => s"on y-axis at $y"
    case (x, y) => s"point ($x, $y)"
  }
  def main(args: Array[String]): Unit = {
    println(quadrant((0, 0)))
    println(quadrant((3, 0)))
    println(quadrant((2, 5)))
  }
}

تفكيك رأس القائمة

object Main {
  def first(xs: List[Int]): String = xs match {
    case head :: tail => s"head=$head, rest=$tail"
    case Nil          => "empty"
  }
  def main(args: Array[String]): Unit = {
    println(first(List(10, 20, 30)))
    println(first(Nil))
  }
}

مطابقة أشكال القوائم الدقيقة

object Main {
  def shape(xs: List[Int]): String = xs match {
    case List()        => "none"
    case List(a)       => s"one: $a"
    case List(a, b)    => s"two: $a, $b"
    case _             => "many"
  }
  def main(args: Array[String]): Unit = {
    println(shape(List()))
    println(shape(List(1)))
    println(shape(List(1, 2)))
    println(shape(List(1, 2, 3)))
  }
}

الاستدعاء التكراري باستخدام الرأس والذيل

object Main {
  def sum(xs: List[Int]): Int = xs match {
    case Nil          => 0
    case head :: tail => head + sum(tail)
  }
  def main(args: Array[String]): Unit = {
    println(sum(List(1, 2, 3, 4)))
  }
}

تفكيك البنى المتداخلة

object Main {
  def main(args: Array[String]): Unit = {
    val data = List(("a", 1), ("b", 2))
    data match {
      case (key, value) :: _ => println(s"first key=$key value=$value")
      case Nil               => println("empty")
    }
  }
}

تجاهل الأجزاء باستخدام _

object Main {
  def main(args: Array[String]): Unit = {
    val triple = (1, 2, 3)
    val (_, middle, _) = triple
    println(s"middle = $middle")
  }
}

ربط أول عنصرين والاحتفاظ بالباقي

object Main {
  def main(args: Array[String]): Unit = {
    val xs = List(1, 2, 3, 4, 5)
    xs match {
      case a :: b :: rest => println(s"a=$a b=$b rest=$rest")
      case _              => println("too short")
    }
  }
}

لماذا نستخدم التفكيك؟

تجميع المفاهيم

object Main {
  def report(scores: List[(String, Int)]): String = scores match {
    case Nil                  => "no scores"
    case (name, pts) :: Nil   => s"only $name with $pts"
    case (name, pts) :: rest  => s"top $name=$pts plus ${rest.size} more"
  }
  def main(args: Array[String]): Unit = {
    println(report(Nil))
    println(report(List(("Ann", 90))))
    println(report(List(("Ann", 90), ("Bo", 80))))
  }
}

اختبار سريع

مراجعة