findViewById


#1

To assign a click listener to view, need to write
findViewById<View>(R.id.resId).setOnClickListener(someClickListener)

If you write without describing generic as View
findViewById(R.id.resId).setOnClickListener(someClickListener)
you will recieve error message

Type inference failed: Not enough information to infer parameter T in 

fun <T : View!> findViewById(id: Int): T!
Please specify it explicitly.

But you need method setOnClickListener in View class. So it easy to parse T:View! as View


#2

Discussed here: https://youtrack.jetbrains.com/issue/KT-28414