Playing around with generics in Kotlin, and thought this was interesting

class Example<T>(private val source: T){
    fun test(value: T?): T? = value
}

fun <T> create() = Example(null)

If we define the class to take in a non-nullable generic type, and still pass in null,

Example(null)

then the generic resolves to

Example<Nothing?>

. If we make the generic nullable

T?

then it resolves to

Example<Nothing>

. I can't find anything online that confirms that null on a generic type returns "Nothing" and I guess it kind of make sense, but can anyone confirm as to how that happens?

you may want to read these posts https://proandroiddev.com/kotlins-nothing-type-946de7d464fb https://blog.kotlin-academy.com/kotlins-nothing-its-usefulness-in-generics-5076a6a457f7

Also note, that by default all generic types extend

Any?

, i.e.

T : Any?

, so

T

can be nullable. You need to write

class Example<T : Any>

if you want that

T

can be non-nullable type only. Then it would make sense to use

T?

in a function inside your class.

Thanks for the answers and the resources!