Hey there. I have following code ``` private su...

# announcements

[df]

Hey there. I have following code

private suspend fun upsertAssets(code: String, assets: List<CreateAssetCommand>): List<UpsertAssetResponse> {
        return assets.chunked(100)
            .map { akeneoClient.upsertAssets(code, it) }
            .fold(mutableListOf()) { acc, next -> acc + next }
    }

that produces the compile time error Type mismatch: inferred type is List<UpsertAssetResponse> but MutableList<UpsertAssetResponse> was expected (the fold line). What am I missing?

[Dominaezzz]

The + doesn't do what you think it does.

[todd.ginsberg]

I think you can replace your fold with flatten().

[df]

flatten sounds good. Would still love to understand why it's not working.

[df]

And when checking the code .plus() does exactly what I expect and I assume + is overloaded correctly.

[todd.ginsberg]

Because when you call +, you get back a List<T>, not a MutableList<T>. Since your fold would be recreating the lists anyway, if you seed it with listOf() instead of mutableListOf(), that would work.

[todd.ginsberg]

(But again, this is what flatten does for you!) 🙂

[df]

already changed it to flatten.. still wanted to understand what's wrong 😉

[df]

thx

[Joel]

s/map/flatMap -> profit

[todd.ginsberg]

Oh man, I spaced out. Yeah, totally. flatMap over map + flatten. Must have not had enough coffee. 😄