CODEWITHSUNDEEP
scala
user5768866
user5768866

Reputation:

Implicit Classes in Scala

Below is the example program for Scala Implicit Class:

object Run {
   implicit class IntTimes(x: Int) {
      def times [A](f: =>A): Unit = {
         def loop(current: Int): Unit =

         if(current > 0){
            f
            loop(current - 1)
         }
         loop(x)
      }
   }
}

There is an other class that calls " 4 times println("hello")" as following, but I can not understand " 4 times println("hello")" mean?

object Demo {
   def main(args: Array[String]) {
      4 times println("hello")
   }
}

Upvotes: 7

Views: 5046

Answers (2)

JasonY
JasonY

Reputation: 770

I also found this example way overly complicated to demonstrate Implicit Classes.

In a nutshell Implicit Classes overwrite other classes with new methods and properties.

In this example, it is overwriting Int to give it a method times. The times method takes a call-by-name parameter with a generic return type:

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

Means f is a function that returns a generic type A.

When a call-by-name variable is used, it calls the function and becomes the return value. Inside times method it is using recursion to loop the call of f the number of times the integer it's called on.

In scala you can call methods by using a dot or space, and no need for brackets for parameters, so object.method(param1, param2) could be object method param1 param2

Hence the final call 4 times println("hello") is actually 4.times(println("hello"))

Upvotes: 6

Buhb
Buhb

Reputation: 7149

4 times println("hello") roughly translates into:

val c = new IntTimes(4)
c.times(println("hello"))

That is, since there is an implicit class that takes an Int as its only argument, with a method times, doing 4.times implicitly instantiates the class with 4 as argument, and then invokes times on it.

Upvotes: 10

Related Questions