Are there ways to restrict the scope of a particul...

# announcements

[Sam Garfinkel]

Are there ways to restrict the scope of a particular extension function to where this is not the receiver? For instance, if I’m wrapping an existing API in a DSL, a fun String.bar() might behave differently depending on what this is. I’m not able to subclass the wrapped API data type as it’s final, and inline classes don’t provide delegates apparently. I thought this would work:

class Foo {
  fun doSomething(it: String) {
    // TODO
  }
}

inline class Bar(val foo: Foo) {
  fun String.doSomething() = doSomething(this)
}

But Bar(Foo()).doSomething("hello") is undefined.

[Sam Garfinkel]

Seems like sort of “ad-hoc” polymorphism is still sort of an area of discussion: https://discuss.kotlinlang.org/t/extension-types-for-kotlin/1390

[Big Chungus]

There is. https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-dsl-marker/

[Evan R.]

Does this work?

fun Bar.barAction() {
    val string = "something"
    string.doSomething()
}

[Evan R.]

String.doSomething() is only valid within the scope of a Bar function

[Sam Garfinkel]

@Big Chungus Yeah I should have specified it is desirable in this case that the outer, non-receiver scope also be referenceable with this. Basically I need a polymorphic receiver like you’d normally get by nesting two apply or with functions.