Scala class extends {}

Question

By chance I came across weird compiling Scala syntax:

class Some extends {
  def hi = println(\"hi\")
}
         


        

Answer 1

Yes this is Scala's structural typing or more commonly known as duck typing.

object LoudDuck {
    def quack(): String = "QUACK"
}

object QuietDuck {
    def quack(): String = "quack"
}

object CowDuck {
    def quack(): String = "moo"
}

def quackMyDuck(duck: { def quack(): String }) {
    println(duck.quack())
}

scala>quackMyDuck(LoudDuck)
QUACK

scala>

scala>quackMyDuck(QuietDuck)
quack

scala>

scala>quackMyDuck(CowDuck)
moo

You can also declare your stuctural types with the "type" keyword.

type Duck = { def quack(): String }

def quackMyDuck(duck: Duck) {
    println(duck.quack())
}