Is there any trick for declare an extension ONLY f...

# announcements

[Davide Giuseppe Farella]

Is there any trick for declare an extension ONLY for nullable type?

class MyClass<T>

MyClass<String?>().myExtension()  // -> OK
MyClass<String >().myExtension()  // -> Does not compile?

[Derek Peirce]

What issue are you running into? MyClass<String?>.myExtension() should not be callable on a MyClass<String> object, unless you're using covariance. Or are you actually asking about MyClass<String>??

[Davide Giuseppe Farella]

I have

interface Asserter<out T> {
    val actual: T?
}

and

infix fun <T : Any?> Asserter<T>.`is`(_null: Null) =
    assertNull(actual)

and I’m expecting to NOT be able to call something like
`assert that "Hello" is Null`

( where assert that "Hello" is Asserter<String )

[Zach Klippenstein (he/him) [MOD]]

I'm not sure if this would actually work (not at a computer rn) but I think you could create an overload of your function that has a non-nullable upper bound (Any) and give it a deprecated annotation with the error level (the coroutine library uses this trick to "capture" invalid calls and suggest alternatives), since the compiler will always select the most specific overload of a method.

You also don't need the Any? bound in this code, it's the implicit upper bound if none is specified because it's the top type.

[Davide Giuseppe Farella]

Wow, seems cool 🙂 I’ll try! thanks!