Creating a method or function in Scala

• In functional programming languages, when you call a function that has parameters, you are said to be applying the function to the parameters

• Scala provides keyword def for creating methods or definitions

/* A definition using 'def' */
def incrementDef = (x: Int) => x + 1

• Declare a method which takes no parameter and returns nothing but prints 'Hello''

def print = println(value)

• Notice that unlike Java, you can ignore curly brackets ({ ... }) while defining Scala methods

def print = { println(value) }

• Declare a method which take a parameter and returns nothing but prints the passed Int value

def printIt(value: Int) = println(value)

• Declare a method which take no parameter and returns something

/* Method returns Int value '1' */
def returnInt = 1

/* Method returns Float value '1.0' */
def returnFloat = 1.0

/* Another way to explicitly define return type (method-name:type) for methods */
def returnInt: Int = return 1
def returnFloat: Float = return 1.0F

• Open program com.inbravo.lang.MethodTest.scala MethodTest.scala

• You can also call a method with variable number of arguments, with the help of star (*)

/* Method which accepts anu number of Int type of arguments */
def sum(args: Int*) = {  

 var result = 0  

 for (arg <- args) result += arg  
  result  
 }
}

/* Multiple valid method calls */
sum(1,2)
sum(1,2,3,4)

• You can define local functions as well in scala just like local fields, and these will be visible in only their enclosing block

• Scala supports named arguments. Each argument is preceded by a parameter name and an equals sign

/* Method definition */
def speed(time : float, distance : float)

/* Method calls with argument names */
speed(distance = 100, time = 10)

Functions are objects

• Perhaps more surprising for the Java programmer, functions are also objects in Scala. It is therefore possible to pass functions as arguments, to store them in variables, and to return them from other functions

• In below example method timeFlies is such a function, which is used as an arguments to another function oncePerSecond

    object Timer {
      def oncePerSecond(callback: () => Unit) {
        while (true) { callback(); Thread sleep 1000 }
      }
      def timeFlies() {
        println("time flies like an arrow...")
      }
      def main(args: Array[String]) {
        oncePerSecond(timeFlies)
      }
    }