تركيب المجالات

بناء نماذج أكبر

case class Money(cents: Long)
case class Product(name: String, price: Money)

object Main:
  def main(args: Array[String]): Unit =
    println(Product("Book", Money(1999)))

تداخل المنتجات

case class Address(city: String, zip: String)
case class Customer(name: String, address: Address)

object Main:
  def main(args: Array[String]): Unit =
    val c = Customer("Ada", Address("London", "E1"))
    println(c.address.city)

التركيب باستخدام المجموعات

case class Item(name: String, qty: Int)
case class Order(id: Int, items: List[Item])

object Main:
  def main(args: Array[String]): Unit =
    val order = Order(1, List(Item("pen", 2), Item("ink", 1)))
    println(order.items.map(_.qty).sum)

تركيب أنواع المجموعات

enum Payment:
  case Card(last4: String)
  case Cash

enum Checkout:
  case Completed(payment: Payment)
  case Abandoned

object Main:
  def main(args: Array[String]): Unit =
    val c: Checkout = Checkout.Completed(Payment.Card("1234"))
    println(c)

دوال تركّب النطاقات

case class Cart(total: Long)
case class Receipt(total: Long, tax: Long)

object Main:
  def checkout(c: Cart): Receipt =
    Receipt(c.total, (c.total * 0.2).toLong)

  def main(args: Array[String]): Unit =
    println(checkout(Cart(1000)))

تركيب عمليات التحقق

object V:
  def name(s: String): Option[String] = if s.nonEmpty then Some(s) else None
  def age(n: Int): Option[Int] = if n >= 0 then Some(n) else None

case class Person(name: String, age: Int)

object Main:
  def make(n: String, a: Int): Option[Person] =
    for nm <- V.name(n); ag <- V.age(a) yield Person(nm, ag)

  def main(args: Array[String]): Unit =
    println(Main.make("Bob", 30))
    println(Main.make("", 30))

الطيّ على البيانات المركبة

case class Line(price: Long, qty: Int)
case class Invoice(lines: List[Line])

object Main:
  def total(inv: Invoice): Long =
    inv.lines.foldLeft(0L)((acc, l) => acc + l.price * l.qty)

  def main(args: Array[String]): Unit =
    val inv = Invoice(List(Line(100, 2), Line(50, 4)))
    println(total(inv))

تحديث النماذج غير القابلة للتغيير

case class Account(id: Int, balance: Long)

object Main:
  def deposit(a: Account, amt: Long): Account =
    a.copy(balance = a.balance + amt)

  def main(args: Array[String]): Unit =
    val a = Account(1, 100)
    println(deposit(a, 50))

نمذجة آلة حالات

enum Light:
  case Red, Green, Yellow

object Main:
  def next(l: Light): Light = l match
    case Light.Red    => Light.Green
    case Light.Green  => Light.Yellow
    case Light.Yellow => Light.Red

  def main(args: Array[String]): Unit =
    println(next(Light.Red))
    println(next(Light.Green))

وضع النطاق والعمليات في طبقات

case class Temp(celsius: Double):
  def toF: Double = celsius * 9 / 5 + 32

object Main:
  def main(args: Array[String]): Unit =
    val t = Temp(25.0)
    println(t.toF)

جمع كل الأجزاء

case class Sku(value: String)
case class Line(sku: Sku, qty: Int)
case class Basket(lines: List[Line]):
  def count: Int = lines.map(_.qty).sum

object Main:
  def main(args: Array[String]): Unit =
    val b = Basket(List(Line(Sku("A"), 2), Line(Sku("B"), 3)))
    println(b.count)

اختبار سريع

مراجعة

case class User(id: Int, name: String)
case class Post(author: User, text: String)

object Main:
  def main(args: Array[String]): Unit =
    val p = Post(User(1, "Ada"), "hello")
    println(p.copy(text = "hi"))