nullable constructor params can be assigned at ini...

# stdlib

[Hullaballoonatic]

nullable constructor params can be assigned at initialization to non-nullable lateinit properties. If they are null, then the property remains uninitialized, otherwise it is set.

class Foo(bar: Int?, baz: Int?, boz: Int?) {
    lateinit var bar: Int = bar // acceptable
    lateinit var baz = baz // implicitly assigned as non-nullable
    lateinit var boz: Int? = baz // unacceptable
}

[Hullaballoonatic]

In general, I just always look for ways to avoid using init block, because I always think it looks really out of place, but as it is currently, afaik, the above logic is only accomplished like this:

class Foo(bar: Int?) {
    lateinit var bar: Int

    init {
        if (bar != null) this.bar = bar
    }
}

[Pavlo Liapota]

At first glance this design looks strange.
Maybe it is better to make property bar nullable? 🙂

[Hullaballoonatic]

it is strange, but it cropped up for me because I was writing an implementation of an interface, and didn't want to make the interface's property nullable

[Pavlo Liapota]

I would use lateinit only in cases when I am sure that variable will be initialized before usage.
How would you work with your variable? You cannot be sure that it will be initialized so would you check isInitialized?

[Hullaballoonatic]

I'm comfortable with it throwing if it isn't initialized at this stage in development

[Pavlo Liapota]

Then you can write something like:

class Foo(
    private val _foo: Int?
) {
    val foo get() = _foo!!
}

[Hullaballoonatic]

yeah, either way is just ugly :S

[Hullaballoonatic]

you'd also have to make _foo a var, and give it a setter to have the functionality of a lateinit var

[Hullaballoonatic]

i imagine that is exactly how lateinit is implemented under the surface