How would I write an extension function for a `T?`...

# getting-started

[chiroptical]

How would I write an extension function for a T? . In Haskell, I use the maybe function pretty frequently. The type is like (default: U, f: (T) -> U, x: T?): U

[chiroptical]

I would really like nullableThing.maybe(default) { x -> … }

[chiroptical]

The closest I have got is nullableThing?.let { x -> …} ?: default which would be the body of the extension function. So, I guess I have two questions: how do I write the extension function and is this really the only way to implement this function?

[chiroptical]

Is there a stdlib function I am missing?

[ephemient]

are you looking to implement something like this? https://kotlinlang.slack.com/archives/C0B8MA7FA/p1669840116773079?thread_ts=1669838883.051849&cid=C0B8MA7FA

[chiroptical]

Yup! Exactly that. Nice

[Pablichjenkov]

Shouldn't it be BAR?

[Pablichjenkov]

Oh no right, when default the block doesn't apply

[chiroptical]

Yeah, I think ?.letWithDefault

[chiroptical]

Would be a nice name.

[chiroptical]

As a Haskeller, I use this function A LOT

[Pablichjenkov]

That's right, by the name I thought the lambda would apply always

[Pablichjenkov]

.letAndApplyOrDefault() perhaps

[chiroptical]

Yeah, I could see that just looking at the type signature. That is one possible implementation.

[Pablichjenkov]

You see that a lot in Kotlin. firstOrNull, lastOrNull

[chiroptical]

I would just call it maybe but that is just how I am used to it being called.

[Pablichjenkov]

I mean naming is hard

[Pablichjenkov]

Got you

[chiroptical]

mapOr isn’t bad

[mkrussel]

The code provided for letWith is broken if R is nullable and block returns null.

[chiroptical]

Oh, because it will always return the default. Good point. You probably want an explicit branch.