this

Learn to access the class itself with this.

this: the current object

The this keyword refers to the current instance inside a method. When a parameter name clashes with a property name, you use this to tell them apart.

class Person(var name: String) {
    fun rename(name: String) {
        this.name = name
    }
}

this.name refers to the property, name to the parameter. The assignment copies the parameter into the property. Using this is not required when there is no clash.

When is this needed?

this is only required when a parameter clashes with a property name. If there is no clash, Kotlin finds the property automatically.

class Person(var name: String) {
    fun rename(newName: String) {
        name = newName  // no need for this
    }
}

newName does not clash with name, so this can be skipped. When there is a clash, this is mandatory; otherwise the assignment goes to the wrong place. You can still use this for clarity even without a clash.

Exercise Add a set method to Person

Define class Person(var name: String); in its body add fun set(name: String) { this.name = name }. In main create val p = Person("Ayşe"), call p.set("Alex") and print p.name with println.

Show example solution

class Person(var name: String) {
    fun set(name: String) {
        this.name = name
    }
}

fun main() {
    val p = Person("Ayşe")
    p.set("Alex")
    println(p.name)
}

Test yourself

Fill in the blank: assign with this

class Person(var name: String) {
    fun set(name: String) {
        ____.name = name
    }
}

Show answer

class Person(var name: String) {
    fun set(name: String) {
        this.name = name
    }
}

When is this used?
- When a parameter clashes with a property name
- Always
- Never
- Only in static methods
Show answer

When a parameter clashes with a property name — answer: when a parameter clashes with a property name. this separates them.
Match expression to meaning

this.name

Property access
name

Parameter
this

Current object
= name

Assignment

Next lesson: Summary - Class basics

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