面向 JavaScript 开发者的 Scala

var a = 2
a *= 2      // 4
a /= 2      // 2

val i = 1     // Int
val d = 1.1   // Double

val a: Byte = 0    // Byte = 0
val a: Double = 0  // Double = 0.0
val a: Float = 0   // Float = 0.0
val a: Int = 0     // Int = 0
val a: Long = 0    // Long = 0
val a: Short = 0   // Short = 0

val x = BigInt(1_234_456_789)
val y = BigDecimal(1_234_456.890)

// map method, long form
List(1,2,3).map(i => i * 10)   // List(10,20,30)

// map, short form (which is more commonly used)
List(1,2,3).map(_ * 10)        // List(10,20,30)

// filter, short form
List(1,2,3).filter(_ < 3)      // List(1,2)

// filter and then map
List(1,2,3,4,5).filter(_ < 3).map(_ * 10)   // List(10, 20)

// create some enumerations that the Pizza class will use
enum CrustSize:
  case Small, Medium, Large

enum CrustType:
  case Thin, Thick, Regular

enum Topping:
  case Cheese, Pepperoni, BlackOlives, GreenOlives, Onions

// import those enumerations and the ArrayBuffer,
// so the Pizza class can use them
import CrustSize.*
import CrustType.*
import Topping.*
import scala.collection.mutable.ArrayBuffer

// define an OOP style Pizza class
class Pizza(
  var crustSize: CrustSize,
  var crustType: CrustType
):

  private val toppings = ArrayBuffer[Topping]()

  def addTopping(t: Topping): Unit =
    toppings += t

  def removeTopping(t: Topping): Unit =
    toppings -= t

  def removeAllToppings(): Unit =
    toppings.clear()

  override def toString(): String =
    s"""
      |Pizza:
      |  Crust Size: ${crustSize}
      |  Crust Type: ${crustType}
      |  Toppings:   ${toppings}
    """.stripMargin

end Pizza

// create a Pizza instance
val p = Pizza(Small, Thin)

// change the crust
p.crustSize = Large
p.crustType = Thick

// add and remove toppings
p.addTopping(Cheese)
p.addTopping(Pepperoni)
p.addTopping(BlackOlives)
p.removeTopping(Pepperoni)

// print the pizza, which uses its `toString` method
println(p)

trait HasLegs:
  def numLegs: Int
  def walk(): Unit
  def stop() = println("Stopped walking")

trait HasTail:
  def wagTail(): Unit
  def stopTail(): Unit

class Dog(var name: String) extends HasLegs, HasTail:
  val numLegs = 4
  def walk() = println("I’m walking")
  def wagTail() = println("⎞⎜⎛  ⎞⎜⎛")
  def stopTail() = println("Tail is stopped")
  override def toString = s"$name is a Dog"

// create a Dog instance
val d = Dog("Rover")

// use the class’s attributes and behaviors
println(d.numLegs)   // 4
d.wagTail()          // "⎞⎜⎛  ⎞⎜⎛"
d.walk()             // "I’m walking"

if (i == 0) {
  println(0)
} else if (i == 1) {
  println(1)
} else {
  println("other")
}

var i = 0
while (i < 3) {
  println(i)
  i += 1
}

// JavaScript
let nums = [1, 2, 3];

// Scala
val nums = List(1, 2, 3)

val day = 1

// later in the code ...
val monthAsString = day match
  case 1 => "January"
  case 2 => "February"
  case _ => "Other"

val numAsString = i match
  case 1 | 3 | 5 | 7 | 9 => "odd"
  case 2 | 4 | 6 | 8 | 10 => "even"
  case _ => "too big"

def isTruthy(a: Matchable) = a match
  case 0 | "" => false
  case _ => true

def isPerson(x: Matchable): Boolean = x match
  case p: Person => true
  case _ => false

val strings = List("a", "b", "c")
val strings = Vector("a", "b", "c")
val strings = ArrayBuffer("a", "b", "c")

val set = Set("a", "b", "a") // result: Set("a", "b")
val map = Map(
  "a" -> 1,
  "b" -> 2,
  "c" -> 3
)

// to, until
(1 to 5).toList                   // List(1, 2, 3, 4, 5)
(1 until 5).toList                // List(1, 2, 3, 4)

(1 to 10 by 2).toList             // List(1, 3, 5, 7, 9)
(1 until 10 by 2).toList          // List(1, 3, 5, 7, 9)
(1 to 10).by(2).toList            // List(1, 3, 5, 7, 9)

('d' to 'h').toList               // List(d, e, f, g, h)
('d' until 'h').toList            // List(d, e, f, g)
('a' to 'f').by(2).toList         // List(a, c, e)

// range method
List.range(1, 3)                  // List(1, 2)
List.range(1, 6, 2)               // List(1, 3, 5)

List.fill(3)("foo")               // List(foo, foo, foo)
List.tabulate(3)(n => n * n)      // List(0, 1, 4)
List.tabulate(4)(n => n * n)      // List(0, 1, 4, 9)

// these examples use a List, but they’re the same with Vector
val a = List(10, 20, 30, 40, 10)      // List(10, 20, 30, 40, 10)
a.contains(20)                        // true
a.distinct                            // List(10, 20, 30, 40)
a.drop(2)                             // List(30, 40, 10)
a.dropRight(2)                        // List(10, 20, 30)
a.dropWhile(_ < 25)                   // List(30, 40, 10)
a.filter(_ < 25)                      // List(10, 20, 10)
a.filter(_ > 100)                     // List()
a.find(_ > 20)                        // Some(30)
a.head                                // 10
a.headOption                          // Some(10)
a.init                                // List(10, 20, 30, 40)
a.last                                // 10
a.lastOption                          // Some(10)
a.slice(2,4)                          // List(30, 40)
a.tail                                // List(20, 30, 40, 10)
a.take(3)                             // List(10, 20, 30)
a.takeRight(2)                        // List(40, 10)
a.takeWhile(_ < 30)                   // List(10, 20)

// map, flatMap
val fruits = List("apple", "pear")
fruits.map(_.toUpperCase)             // List(APPLE, PEAR)
fruits.flatMap(_.toUpperCase)         // List(A, P, P, L, E, P, E, A, R)

val nums = List(10, 5, 8, 1, 7)
nums.sorted                           // List(1, 5, 7, 8, 10)
nums.sortWith(_ < _)                  // List(1, 5, 7, 8, 10)
nums.sortWith(_ > _)                  // List(10, 8, 7, 5, 1)

List(1,2,3).updated(0,10)             // List(10, 2, 3)
List(2,4).union(List(1,3))            // List(2, 4, 1, 3)

// zip
val women = List("Wilma", "Betty")    // List(Wilma, Betty)
val men = List("Fred", "Barney")      // List(Fred, Barney)
val couples = women.zip(men)          // List((Wilma,Fred), (Betty,Barney))

let stuff = ["Joe", 42, 1.0];

val a = ("eleven")
val b = ("eleven", 11)
val c = ("eleven", 11, 11.0)
val d = ("eleven", 11, 11.0, Person("Eleven"))

d(0)   // "eleven"
d(1)   // 11

enum Color:
  case Red, Green, Blue

enum Color(val rgb: Int):
  case Red   extends Color(0xFF0000)
  case Green extends Color(0x00FF00)
  case Blue  extends Color(0x0000FF)

enum Planet(mass: Double, radius: Double):
  case Mercury extends Planet(3.303e+23, 2.4397e6)
  case Venus   extends Planet(4.869e+24,6.0518e6)
  case Earth   extends Planet(5.976e+24,6.37814e6)
  // more planets here ...

  private final val G = 6.67300E-11
  def surfaceGravity = G * mass / (radius * radius)
  def surfaceWeight(otherMass: Double) = otherMass * surfaceGravity

// show an alert dialog on a button click
jQuery("#hello-button").click{() =>
  dom.window.alert("Hello, world")
}

// define a button and what should happen when it’s clicked
val btn = button(
  "Click me",
  onclick := { () =>
    dom.window.alert("Hello, world")
  })

// create two divs with css classes, an h2 element, and the button
val content =
  div(cls := "foo",
    div(cls := "bar",
      h2("Hello"),
      btn
    )
  )

// add the content to the DOM
val root = dom.document.getElementById("root")
root.innerHTML = ""
root.appendChild(content.render)