How to write an internal extension function for an...

# getting-started

[lesincs]

How to write an internal extension function for an existing class? See thread.

[lesincs]

if I have a Foo class, I can write an internal extension function for String, and I can use this extension function only in the Foo scope.

class Foo {
  fun String.greet(): String {
    return "Hello$this"
 }
}

fun main() {
  with(Foo()) {
    "str".greet()
 }
}

But what if the Foo class is in some library, how do I achieve the same functionality?

[Javier]

context receivers is what you are looking for and they are not available

[lesincs]

I see, thank you. Follow your information, I just found this reference: https://github.com/Kotlin/KEEP/issues/259

[CLOVIS]

The closest thing you can have at the moment is to create a value class that wraps the class you don't control, and create an extension method there. However... I don't really think that will lead to nice code. Until context receivers are added, you're probably stuck with making it a normal method.