Is there an annotation like `@Deprecated` but mean...

# announcements

[Rob Elliot]

Is there an annotation like @Deprecated but meaning specifically that a method call is pointless, because it returns this and has the same return type as the object it is called on?

For instance, String.toString() = this would be a candidate for it.

[Rob Elliot]

You would do this when the method is defined as an abstract one on a supertype - so it’s totally valid to call it on the supertype, and the subtype’s = this implementation is totally correct, but it would never make sense to call it on an instance types as the subtype.

[christophsturm]

maybe method contracts can do it?

[Byron Katz]

I usually put something like throw IllegalAccessError() inside a method like that, but I don't know if there is an annotation.

[Rob Elliot]

I definitely don’t want that:
1) I want a compile time warning/error, not a runtime one
2) It would be very surprising & undesirable if calling the method on a val typed as the supertype blew up just because it happened to be an instance of a particular subtype

The goal is just to gently point out to developers that they are making an unnecessary call, like calling "a string".toString(). You wouldn’t want the implementation of toString on String to throw an exception rather than returning itself.

[christophsturm]

I think idea could just do that without any annotation

[spand]

Isnt this just:

@Deprecated("Useless method call", replaceWith = ReplaceWith("this"), level = DeprecationLevel.ERROR)

[Rob Elliot]

Yes, that’s what I’m doing; it’s just that @Deprecated feels slightly semantically odd for a method that exists for good reason and that I have no intention of ever removing, and that it’s quite valid to call on the supertype.

So I was wondering if there was something more like @PointlessToCall that had the same effect..

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

You can define your own annotations annotated with RequiresOptIn that kind of act like Deprecated.