vvviiimmm

implicit val bob = "Bob"

def greet(implicit name: String) = {
  println(s"Hello, $name!")
}

// usage
greet

// outputs "Hello, Bob!"

vvviiimmm

implicit val bob = "Bob"
implicit val alice = "Alice"

def greet(implicit name: String) = {
  println(s"Hello, $name!")
}

// usage
greet

vvviiimmm

implicit def intToStr(num: Int): String = s"The value is $num"

42.toUpperCase() // evaluates to "THE VALUE IS 42"

def functionTakingString(str: String) = str

// note that we're passing int
functionTakingString(42) // evaluates to "The value is 42"

vvviiimmm

object Helpers {
  implicit class StringOps(str: String) {
    def yell = str.toUpperCase() + "!"
    def isQuestion = str.endsWith("?")
  }
}

"Hello world".yell // evaluates to "HELLO WORLD!"
"How are you?".isQuestion // evaluates to 'true'

vvviiimmm

case class StringOps(str: String) {
  def yell = str.toUpperCase() + "!"
  def isQuestion = str.endsWith("?")
}

vvviiimmm

case class StringOps(str: String) {
  def yell = str.toUpperCase() + "!"
  def isQuestion = str.endsWith("?")
}

implicit def stringToStringOps(str: String): StringOps = StringOps(str)

"Hello world".yell // evaluates to "HELLO WORLD!"
"How are you?".isQuestion // evaluates to 'true'

vvviiimmm

// Our interface
trait Monoid[A] {
  def zero: A
  def plus(a: A, b: A): A
}

// Implementation for integers
implicit object IntegerMonoid extends Monoid[Int] {
  override def zero: Int = 0
  override def plus(a: Int, b: Int): Int = a + b

vvviiimmm

def sum[A](values: Seq[A])(implicit ev: Monoid[A]): A

def sum[A:Monoid](values: Seq[A]): A

vvviiimmm

def sum[A:Monoid](values: Seq[A]): A = {
  val ev = implicitly[Monoid[A]]
  values.foldLeft(ev.zero)(ev.plus)
}

vvviiimmm

 def implicitly[T](implicit e: T) = e