Use `buildSequence`

# getting-started

[diesieben07]

Use buildSequence

[poohbar]

right but thats scary coroutines right

[diesieben07]

Coroutines are great! 😄

[diesieben07]

It's in the stdlib, too

[diesieben07]

Then you can just write a for loop and yield

[poohbar]

ok so lets say i have code like this

[arekolek]

it’s no longer experimental? 😉

[poohbar]

var offset = 0
val items = mutableListOf<Map<*, *>>()
while (true) {
    val chunk = queryRunner.query("SELECT id FROM item LIMIT 10000 OFFSET $offset")
    if (chunk.isEmpty()) {
        break
    }
    items.addAll(chunk)
    offset += 10000
    println("Loaded $offset rows")
}

[poohbar]

and i would like to rewrite is as sequence

[Egor Trutenko]

@arekolek no, they're 1.0.0 as soon as Kotlin 1.3 is released

[marstran]

buildSequence has been renamed sequence in 1.3 by the way

[arekolek]

with a local variable, this should do:

var offset = 0
return generateSequence {
    queryRunner.query("SELECT id FROM item LIMIT 10000 OFFSET $offset")
            .takeUnless { it.isEmpty() }
            .also { offset += 10000 }
}
        .flatten()

[poohbar]

thanks

[arekolek]

Here’s a way without the variable and without pair:

generateSequence(0) { it + 10000 }
        .map { queryRunner.query("SELECT id FROM item LIMIT 10000 OFFSET $it") }
        .takeWhile { it.isNotEmpty() }
        .flatten()