Screenshot 2018-11-06 at 8.14.57 PM.png

# announcements

[vibin]

Screenshot 2018-11-06 at 8.14.57 PM.png

[Vladyslav Sitalo]

I expect you want something like initialValue: T?

[vibin]

I want the caller to decide the nullability of T

[vibin]

So ObservableField("").get() returns non-null type, but ObservableField(null).get() returns nullable type

[vibin]

This is what I want to achieve, is it possible?

[dalexander]

That should be possible. This example behaves as expected:

fun main() {
    val d1 = Demo<String>("asdf")
    val d2 = Demo<String?>(null)
    
    onlyAcceptsNonNullableStrings(d1.getItem())
    // onlyAcceptsNonNullableStrings(d2.getItem()) // This is a compiler error
}

fun onlyAcceptsNonNullableStrings(value: String) {
    //do whatever
}

class Demo<T>(private val item: T) {
    fun getItem(): T {
    	return item
    }
}

Maybe remove the upper bound from your class definition?

[Shawn]

no, I don’t think this can work with that secondary constructor

[Shawn]

like if you call ObservableField<String>(), how does that work?

[Shawn]

you can’t call this(null) if T is String

[dalexander]

Right, in that case with the secondary constructor that won’t be possible because Any is kind of a subclass of Any? so that’s not always going to be a legal call, because T could be non-nullable.

[dalexander]

https://www.kotlindevelopment.com/typical-kotlin/ has some useful information about how nullable types work

[Dico]

I believe the code shown initially will work with experimental (new) type inference in kotlin 1.3.

[vibin]

ooh, I’ll try it out, thanks!

[dsavvinov]

@Dico I don’t think it’s going to work in NI, because it has nothing to do with inference to begin with (all types are explicitly written down here).

This is an ordinary type-checking, and it should fail because of reasons already mentioned above.

[Dico]

Oh, I'm an idiot. Excuse me 😀

[dsavvinov]

Totally no problem, we all humans here 👌

[ilya.gorbunov]

A similar idea was discussed in the forum before: https://discuss.kotlinlang.org/t/nulls-and-generics/2219
Perhaps it's time to create a feature request out of that.

[vibin]

thanks for the link!