The this keyword is used to refer to the object that we are currently talking about. In our current Person example, the this keyword refers to the Person object. Take a Person class example and append the this keyword with each property:

class Person(pName: String, pAge: Int, pHeight : Double ) {
     var name : String
     var age : Int
     var height : Double
     init {
         this.name = pName
         this.age = pAge
         this.height = pHeight
     }
 }

The this keyword refers to the name, age, and height properties of the current object. The this keyword is optional and the main reason to use it is to remove the ambiguity between the class property and the local parameter. 

Create a simple form of the Person class with one property name and pass a constructor parameter with a similar name:

class Person(name: String) {
     var name : String
     init{
         name = name
    }
 }

This situation would be confusing for the Kotlin compiler and it would throw two errors:

• Property name must be initialized: This is the error regarding the class property
• val cannot be reassigned: This error is within the init block

The Kotlin compiler cannot distinguish between the class property and the constructor parameter, so the this keyword plays a vital role in this situation because it refers to the current object. Adding this.name tells the compiler that the name is a class property. You must use the this keyword inside the init method to avoid the ambiguity and improve code readability:

class Person(name: String, age: Int, height : Double ) {
    var name : String
    var age : Int
    var height : Double

    init {
        this.name = name
        this.age  = age
        this.height = height
    }
}

fun main(args: Array<String>) {
    val abid = Person("Abid", 40, 6.0)
    println("Name ${abid.name}, Age ${abid.age} Height ${abid.height}")
}

The this keyword is also used when a class contains more than one constructor, and it is required to call one constructor from within another constructor:

The output of the program doesn't change, but the this keyword increases the readability of the code.