Hello I’m working on an hobby oss project, ‘parti...

# functional

[Jun Sekine]

Hello

I’m working on an hobby oss project, ‘partial-function-kt’, which is a Kotlin analogue of Scala’s PartialFunction. Would you kindly be willing to share your thoughts, suggestions, or any feedback on this implementation? Or, if you have any good precedents, could you please share them with me?

https://github.com/jsoizo/partial-function-kt

[Daniel Pitts]

Interesting concept. I personally don't like using null as a result in these cases, but it would probably take considerable rework to implement safely without nulls.

[Daniel Pitts]

Stylistically, I'd also consider making andThen and orElse infix functions.

[Daniel Pitts]

I would also consider creating a single reusable class for use in the builder functions:

class SimplePartialFunction<A, B>(
    val isDefinedAtLambda: (A) -> Boolean,
    val applyLambda: (A) -> B
) : PartialFunction<A, B> {
   override fun isDefinedAt(a: A): Boolean = isDefinedAtLambda(a)
   override fun apply(a: A) = applyLambda(a)
}

fun partialFunction(isDefinedAt: (A) -> Boolean, apply: (A) -> B): PartialFunction<A,B> = 
    SimplePartialFunction(isDefinedAt, apply)

[Daniel Pitts]

I think I'd change the names of the extensions as well. I think you should use Iterable.mapDefined and Iterable.firstDefined for clearer meaning. Don't forget to add support for Sequence 😉

[Daniel Pitts]

BTW, if you're willing, I also have a small project I'd like feedback on. Posted here

[Jun Sekine]

@Daniel Pitts Thanks for the good feedback. Some of the feedback I have received will be incorporated into the code.