How to write an internal extension function for an existing kotlinlang #getting-started

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Title

lesincs

09/13/2021, 12:27 PM

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

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

09/13/2021, 12:45 PM

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

lesincs

09/13/2021, 12:51 PM

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

CLOVIS

09/16/2021, 5:08 PM

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.

👍 1

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