Extension fields in Kotlin

Question

It's easy to write extension methods in Kotlin:

class A { } class B {     fun A.newFunction() { ... } } 

But is there some way to create extension variable? Like:

class B {     var A.someCounter: Int = 0 } 

Answer 1

You can create an extension property with overridden getter and setter:

var A.someProperty: Int   get() = /* return something */   set(value) { /* do something */ } 

But you cannot create an extension property with a backing field because you cannot add a field to an existing class.