Kotlin annotate receiver of extension function

Question

I would like to restrict on which constant value extension function can be called. For example function like:

@IdRes
fun <T : View> Int.find() = findViewById<T>(this)

If this was called on real id, it's fine:

R.id.someView.find<TextView>() // ok

But this should make compilation error:

42.find<TextView>() // should be compile error

Is annotating extension receiver supported in Kotlin?

yole · Accepted Answer · 2018-07-03 14:15:00Z

14

As described in the documentation, you can use the following syntax:

fun @receiver:IdRes <T : View> Int.find() = ...

However, note that the Kotlin compiler is not aware of the semantics of the Android annotations, so their incorrect use is never a compilation error; it's at best a failed lint check.

answered Jul 3, 2018 at 14:15

yole

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2 Comments

xinaiz Over a year ago

This doesn't highlight the call when R.color.colorPrimary.find() is used

yole Over a year ago

Most likely the lint checks don't handle annotations on the receiver. You can file an issue in the Android issue tracker.

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