CODEWITHSUNDEEP
scala
user1050619
user1050619

Reputation: 20856

High order functions in Scala

IM trying to understand the below high order functions in Scala but need some clarifications on the parameters of the functions.

Questions:-

  1. What does the Int => String in the apply function mean? v: Int indicates that the parameter v is of type Int.

  2. What does the [A](x: A) mean in layout function?

     object Demo {
   def main(args: Array[String]) {
    println( apply( layout, 10) )
  }

   def apply(f: Int => String, v: Int) = f(v)

   def layout[A](x: A) = "[" + x.toString() + "]"
}

Upvotes: 1

Views: 155

Answers (2)

Johnny
Johnny

Reputation: 15413

The syntax of Int => String means passing a function that accepts Int and returns String.

Here is a useful example for passing function:

case class Person(name: String, lastName: String)

val person = Person("Johnny", "Cage")

def updateName(name: String) = {
  updatePerson(_.copy(name = name))
}

def updateLastName(lastName: String) {
  updatePerson(_.copy(lastName = lastName))
}

private def updatePerson(transformer: Person => Person): Unit = {
  transformer(person)

}

Note how each update function passes the copy constructor.

Upvotes: 0

nmat
nmat

Reputation: 7591

f: Int => String means that f is a function with one argument of type Int and with a return type String

def layout[A](x: A) means that parameter x is of type A, which can be of any type. Here are a couple of examples on how to invoke layout:

layout[String]("abc") //returns "[abc]"
layout[Int](123)  //returns "[123]"

When main runs it invokes apply with the layout function and the argument 10. This will output "[10]"

Upvotes: 10

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