Scala Docs Implicit Class Example

Question

I'm looking at the implicit class example in the Scala Docs:

object Helpers {
 implicit class IntWithTimes(x: Int) {
  def times[A](f: => A): Unit = {
  def loop(current: Int): Unit =
    if(current > 0) {
      f
      loop(current - 1)
    }
  loop(x)
  }
 }
}

Can someone please explain this syntax and functionality?

times[A](f: => A)

Sascha Kolberg · Accepted Answer · 2015-09-18 18:37:25Z

3

def times[A](f: => A): Unit

is a function signature, where A is a generic type parameter. It is unbound, thus it can be Any'thing.

f: => is a by name parameter. That is the f is not evaluated when the function time is called but only every time it is called within time.

This is a good post about calling-by-name.

So in the example, if you have the implicit class in your scope you can do:

var count = 0
5 times { count += 1; println(count) }

and would get

as output.

answered Sep 18, 2015 at 18:37

Sascha Kolberg

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Comments

Rado Buransky · Accepted Answer · 2015-09-18 18:27:46Z

1

times is a polymorphic function which takes a single type parameter A and a single value parameter f. f is function which has result of type A. A function which takes another function as a parameter is called a higher-order function.

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