are there any advantages using Optional rather than nullable type?

# announcements

[E.Kisaragi]

are there any advantages using Optional rather than nullable type?

[Shawn]

in Kotlin? not really, since you can do all the fun monadic stuff with ?. and the scope functions

[Shawn]

assuming you mean java.util.Optional, that is, the only real reason to use it is for java compatibility, afaict

[Shawn]

but, there are some more strongly-enumerated Option/Maybe monads that folks have written for Kotlin, and they have their own benefits

[E.Kisaragi]

like flatMap or something?

[Shawn]

eh, flatMap isn’t really a thing you have to deal with nullables and safe navigation, the benefits I’m talking about are things like potentially more expressive APIs or different kinds of pattern matching

[streetsofboston]

Like the ones from Arrow, where Optional is a monadic type as well, while T? isn’t .

[Shawn]

https://arrow-kt.io/docs/0.10/apidocs/arrow-core-data/arrow.core/-option/index.html is a good read to get a handle on what a dedicated Option monad can provide

[Zach Klippenstein (he/him) [MOD]]

A pretty big advantage of Optional types is they let your type parameter be nullable itself. Otherwise you need to use a null sentinel, which can be awkward.

[streetsofboston]

Some of the nullability is a bit weird. Eg this does not compile:

class MyClass<T : Any?>() {
    val optionalValue: T? get() { TODO() }
    
    fun doSomething(callback: (T) -> Any) {
        callback(optionalValue)
    }
}

[streetsofboston]

But this does (with an unchecked cast warning) and won’t throw null-pointer-exceptions:

class MyClass<T : Any?>() {
    val optionalValue: T? get() { TODO() }

    fun doSomething(callback: (T) -> Any) {
        callback(optionalValue as T)
    }
}

I guess there are such things as T?? types? 🙂

[Mike]

IIRC, Arrow is deprecating Option, and using null features instead.

[E.Kisaragi]

@streetsofboston
btw why do you cast T?? (which is T? actually) into T... I'd throw NoSuchElemException like java.

[streetsofboston]

@E.Kisaragi My first code sample does not compile. The second example should not need a cast of optionalValue as T, since T has an upper bound of Any? (not Any) and Any? allows for null values... no need for throwing a NoSuchElementException, I just want to send callback a null when the value is null...

[E.Kisaragi]

oh okay