Property Accessor

If you are new to Kotlin, there is something in property accessor that you might find it interesting. There are two methods - get() for getter and set() for setter for each property.

var a: Int = 0
  get() {
    return field
  }
  set(value) {
    field = value
  }

The default behaviour for a property returns its stored value from a getter and modifies it with a setter. Inside those, the stored value is manipulated indirectly using the field keyword and they are only valid within these two functions.

If we set a property as private, both get() and set() will also become private. For best practice, we usually make setter function as private whereas getter function will be exposed as public. In that way, the property is allowed to read outside the class, however, the value can only be modified within the same class.

class Balance {
  var value: Int = 0
    private set

  fun inc() = value++
  fun dec() = value--
}

class Client() {
  val balance = Balance()
  balance.inc() // this will increase the balance
  print(balance.value)
}