bijancn

val x = "Hello"
val r1 = x + " World"
val r2 = x + " World"

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val x = new java.lang.StringBuilder("Hello")
val r1 = x.append(" World").toString
val r2 = x.append(" World").toString

bijancn

var x = 42
x = x + 1

bijancn

val x = new java.lang.StringBuilder("Hello")
val r1 = x.append(" World").toString
// 'Hello World'
val r2 = x.append(" World").toString
// 'Hello World World'

bijancn

val r1 = (new java.lang.StringBuilder("Hello")).append(" World").toString
// 'Hello World'
val r2 = (new java.lang.StringBuilder("Hello")).append(" World").toString
// 'Hello World'

bijancn

object Cafe {
  //@JavaPeople: We don't need semicolons or the return keyword
  def buyCoffee(creditCard: CreditCard): Coffee = {
    val cup = new Coffee()         // new coffee is created
    creditCard.charge(cup.price)   // side effecting call to outside
    cup                            // cup is returned
  }
}

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object Cafe {
  def buyCoffee(creditCard: CreditCard): (Coffee, Charge) = {
    val cup = new Coffee()                // new coffee is created
    (cup, Charge(creditCart, cup.price))  // cup and charge is returned
  }
}
// Can be created without new keyword
case class Charge(creditCard: CreditCard, amount: Double)

bijancn

Cafe.buyCoffee(creditCard) shouldBe (coffee, charge)

bijancn

def count(p: A => Boolean): Int

def find(p: A => Boolean): Option[A]

def filter(p: A => Boolean): List[A]

def exists(p: A => Boolean): Boolean

def forall(p: A => Boolean): Boolean

bijancn

def loadNumberOfItems(url: String): IO[Either[Exception, Int]] = {
  val maybeUrl: Option[Url] =
    Url(url)
  val eitherUrl: Either[Exception, Url] =
    maybeUrl.toRight(InvalidUrl)
  val eitherJson: Either[Exception, IO[Json]] =
    eitherUrl.map(u => request(u))
  val eitherResult: Either[Exception, IO[Either[Exception, Int]]] =
    eitherJson.map(futureJson =>
      futureJson.map(json => json.getFieldOption("number").flatMap(x => x.as[Int]).toRight(InvalidJson)))