Operator Overloading in Scala

Operators like +, – , * and so on are actually not operators in traditional sense in Scala language. They all are methods. :). Scala language provides a relaxed syntax when it comes to method invocations. The dot (.) and braces between the objects and method names are optional. When you say object1 + object2 it actually is translated into object1.+(object2).

Therefore operator overloading in Scala means implementing a method with the operator as the name of the method. Let’s learn this with an example. We’ll create a class called Shape with height and width variables. We’ll implement the + and * methods as shown below.

class Shape(private val theHeight:Int,private val theWidth:Int){
  val height = theHeight;
  val width = theWidth;
  def +(another:Shape):Shape = {
     new Shape(this.height+another.height,this.width+another.width)
  }
  def *(another:Shape):Shape = {
	new Shape(this.height*another.height,this.width*another.width)	  
  }
}

You can invoke the + and * methods on Shape objects as shown below.

var shape1 = new Shape(10,20)
var shape2 = new Shape(30,20)
var shape3 = shape1 + shape2
println(shape3.height + ", " + shape3.width)//Prints 40,40

var shape4 = shape1 * shape2
println(shape4.height + ", " + shape4.width)//Prints 300,400

You can invoke + and * methods together. You don’t have operator precedence in Scala however. Instead Scala has method priorities. If you invoke multiple methods in a single statement the asterik, slash characters are given high priority followed by the plus, minus and so on. The methods with letters have the least priority. So if you have a method call like this obj1 + obj2 * obj3 foo(obj4). The asterik method is invoked first, followed by plus and finally the foo method is called.

 var s1 = new Shape(10,20)
 var s2 = new Shape(30,40)
 var s3 = new Shape(50,60)
 var s4 = s1 + s2 * s3 
 println(s4.height + ", " + s4.width) //Prints 1510,2420