Want to understand (more deeply) the purpose of `b...

# getting-started

[Shehab Ellithy]

Want to understand (more deeply) the purpose of buildList and family. To me it's semantics instead of (the written-on-phone hence untested block)

mutableListOf<Int>().run {
    add(1)
    this as List<Int>
}

Here're the advantages I see:
1. `buildList`'s usage, semantically, is clearer
2. No need to cast (but can just specify the type somewhere)
3. buildList (after the work on the Builder annotation) can infer types so no need to specify any types explicitly
Am I missing something else?
Pure judgment call here, but isn't the work on ListBuilder and builder annotation too much just for this?
Only point 3 to me seems that worth it to include directly in the language

[ephemient]

buildList behaves more like

mutableListOf<Int>().run {
    add(1)
}.toList()

because the resulting list is actually immutable, not just by the List type, but also by overriding the mutation methods (since the underlying java.util.List interface methods may be accessed despite the kotlin.collections.List interface not containing them)

[ephemient]

but unlike that snippet, it does so without the extra list copy

[ephemient]

it also provides a nice, consistent, parallel API to other more complex ones such as the flow builder which really doesn't have a good alternative

[Shehab Ellithy]

So efficiency is a goal too. Not sure what flow builder is (and Google not helping)

[ephemient]

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.sequences/sequence.html, https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/flow.html, https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/produce.html, etc.

[Shehab Ellithy]

I see. Didn't know they're called flow builders

[ephemient]

only the flow one is a flow builder, the others are just builders in the same style

[ephemient]

(that similarly can't be easily represented otherwise)

[Shehab Ellithy]

So, I'm guessing, there was a need to build (relatively large) immutable lists efficiently thats why this came about

[Shehab Ellithy]

Still doesn't feel too good...

[ephemient]

https://youtrack.jetbrains.com/issue/KT-15363

[ephemient]

why doesn't it?

[Shehab Ellithy]

Ok that YouTrack makes a lot more sense, thanks!