Extension fields in Kotlin

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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

No - the href="https://kotlinlang.org/docs/reference/extensions.html"
rel="noreferrer">documentation explains
this:

Extensions do not actually modify classes they extend. By defining an
extension, you do not insert new members into a class, but merely make new functions
callable with the dot-notation on instances of this
class.

and

Note that, since extensions do not actually insert members into classes,
there’s no efficient way for an extension property to have a backing field. This is why
initializers are not allowed for extension properties. Their behavior can only be
defined by explicitly providing
getters/setters.

Thinking
about extension functions/properties as just syntactic sugar for calling a static
function and passing in a value hopefully makes this clear.