Scalaの=>の使われ方

def calculate(input: => Int) = input * 37

val taro = "Taro"
// taro: String = "Taro"

taro match {
  case "Taro" => "Male"
  case "Jiro" => "Male"
  case "Hanako" => "Female"
}

val add = (x: Int, y: Int) => x + y

def double(n: Int, f: Int => Int): Int = {
  f(f(n))
}

import users.{UserPreferences => UPrefs} 

trait User {
  def username: String
}

trait Tweeter {
  this: User =>  // thisが再割り当てされます
  def tweet(tweetText: String) = println(s"$username: $tweetText")
}

class VerifiedTweeter(val username_ : String) extends Tweeter with User {  // TweeterがUserを必要とするためミックスインします。
	def username = s"real $username_"
}

val realBeyoncé = new VerifiedTweeter("Beyoncé")
realBeyoncé.tweet("Just spilled my glass of lemonade")  // "real Beyoncé: Just spilled my glass of lemonade"と出力します。

def func1(num: Int): (=> Int) => Int = { r =>
  {
    println("func1 start")
    r * num
  }
}

def func2(num: Int): Int => Int =
  sdadsar => {
    println("func2 start")
    sdadsar * num
  }

def func3(num1: Int)(num2: Int) = num1 * num2

val getFour = () => {
  println("four")
  4
}

val result1 = func1(2)(getFour())
val result2 = func2(2)(getFour())
val result3 = func3(2)(4)

println(result1) // 8
println(result2) // 8
println(result3) // 8