Scala – Nested Function

In Scala, a function defined inside another function is called nested function or local function. This feature is not supported by Java. In other languages, we can call a function from another function but that is not nested function. Multiple function definitions can be defined inside parent function.Let’s understand this with examples.

Example1:

A function named calculation has been written and inside that multiple nested functions have been created as shown below. These nested function will do different calculations and print the result.

object nestedFunc {

  def main(args: Array[String]): Unit = {
    //calling Function
    calculate(3,2)
  }
  //Function
  def calculate(a:Int,b:Int): Unit ={
    //Nested Function
    def add(): Unit ={
      println("Addition of a and b is " + (a + b))
    }
    //Nested Function
    def mul(): Unit ={
      println("Multiplication of a and b is " + (a * b))
    }
    //Nested Function
    def sub(): Unit ={
      println("Subtraction of a and b is " + (a - b))
    }
    add()
    mul()
    sub()
  }
}

Output:
Addition of a and b is 5
Multiplication of a and b is 6
Subtraction of a and b is 1

A nested function can be defined inside another function and so on. It is called nesting of function. Theoretically, nesting is possible to unlimited depth but practically it id done to few levels.Let’s see an example below where nesting is done till 3rd level.

Example2:

object nestedFunc {

  def main(args: Array[String]): Unit = {
    //calling Function
    CarDetails()
  }
  //Function
  def CarDetails(): Unit ={
    model()
    //first Nested Function
    def model(): Unit ={
      println("What is the model of the car?")
        color()
        //Second Nested Function
        def color(): Unit ={
          println("What is the color of car?")
          price()
            //Third Nested Function
            def price(): Unit ={
              println("What is price of the car?")
            }
        }
    }
  }
}

Output:
What is the model of the car?
What is the color of car?
What is price of the car?

Example3:

In the below example, function is doing factorial of given number. A nested function named fact is defined inside parent function named factorial.

object NestedFunc2 {

  def main(args: Array[String]): Unit = {
    println("factorial of 3 is " + factorial(3));
    println("factorial of 5 is " + factorial(5));
  }

  def factorial(x: Int): Int = {
    def fact(x: Int, accumulator: Int): Int = {
      if (x <= 1) accumulator
      else fact(x - 1, x * accumulator)
    }
    fact(x, 1)
  }
}

Output:
factorial of 3 is 6
factorial of 5 is 120