The Kotlin extension function is a new feature of Kotlin. Without creating an object of class. It is known as an extension function. To add an extension function to a class define a new function appended to the class name as shown in the following example.
Example:
// A sample class to demonstrate extension functions
class Circle (val radius: Double){
// member function of class
fun area(): Double{
return Math.PI * radius * radius;
}
}
fun main(){
// Extension function created for a class Circle
fun Circle.perimeter(): Double{
return 2*Math.PI*radius;
}
// create object for class Circle
val newCircle = Circle(2.5);
// invoke member function
println("Area of the circle is ${newCircle.area()}")
// invoke extension function
println("Perimeter of the circle is ${newCircle.perimeter()}")
}
Output
The area of the circle is 34954084936208
The perimeter of the circle is 15.707963267948966
Extended library class using an extension function
Kotlin not only allows the user-defined classes to extend but also the library classes. The following example of library functions.
Example:
fun main(){
// Extension function defined for Int type
fun Int.abs() : Int{
return if(this < 0) -this else this
}
//abs method called
println((-508).abs())
//abs method called
println(508.abs())
}
Output
508
508
Happy coding!