Hope this is the right channel to ask this. I’m t...

# functional

[bbaldino]

Hope this is the right channel to ask this. I’m trying to figure out the correct way to “flatten” nested Result types. I have a method like this:

fun one(): Result<SomeType> {
    return two()
        .map { someOtherType ->
            three(someOtherType)
                .map { someType -> 
                    doSomethingWithSomeType(someType)
                    someType
}

fun two(): Result<SomeOtherType> { ... }
fun three(someOtherType: SomeOtherType): Result<SomeOtherOtherType> { ... }

the compiler complains that I’m returning Result<Result<SomeType>> instead of Result<SomeType>, which I think I get…I just can’t remember the right way combination of `map`/`fold`/something else to “flatten” the result?

[Richard Gomez]

I think you want is flatMap. Think of flatmap as "and then", whereas map is "transform value".

[bbaldino]

That was my first thought as well, but there doesn’t seem to be a flatMap defined on Result?

[Richard Gomez]

Ah, shoot. I'm getting recommendations from Kotest:
https://github.com/kotest/kotest/blob/c064f148f6b50af6999a000e82d43a42dd8a066f/kotest-common/src/commonMain/kotlin/io/kotest/common/results.kt

[Richard Gomez]

I generally avoid the built-in Result type because it lacks a lot of features, and prefer something like https://github.com/michaelbull/kotlin-result/ instead

[bbaldino]

Ah ok. Yes I was all excited to hear Result as a return had been stabilized, but since then I think every discussion I’ve read about it has had at least one person pointing to that lib 🙂

[bbaldino]

Does look like a nice API…I think I’ll give it a shot. Thanks!