Scope

In nested scopes, we may wish to refer to an outer instance. To do that, we must qualify the usage of this, and we do that using labels. The label we use is typically the name of the outer class, but there are more complicated rules for functions and closures as discussed in Chapter 5, Higher-Order Functions and Functional Programming.

Consider the following code:

    class Building(val address: String) { 
      inner class Reception(telephone: String) { 
        fun printAddress() = println(this@Building.address) 
      } 
    } 

Note that the print function needed to qualify access to the Building outer instance. This is because this inside the printAddress() function would have referred to the closest containing class, which, in this case, is Reception. Do not worry about the inner keyword—that will be covered in Chapter 3, Object-oriented Programming in Kotlin.