We have a detekt rule against nested block depth. ...

# getting-started

[Colton Idle]

We have a detekt rule against nested block depth.

Rather than surpressing it I want to maybe simplify some things. I'm wondering if two inner ForEach statements can be simplified into 1 somehow?

e.g.

outerList.forEach { outerItem ->
    innerList.forEach { innterItem ->

[Sam]

Using flatMap on a Sequence is one general pattern for expressing this sort of nested loop without the nesting

[Sam]

outerList.asSequence().flatMap { innerList.asSequence() }.forEach { ... }

Not sure it's exactly simpler, though...

[Landry Norris]

How deep is this? I'd be looking if I can extract anything higher to a method first.

[Colton Idle]

Detekt complains at 4.
i basically have two forEach loops, and then two nested ifs

[Colton Idle]

so full method looks like this essentially

outerList.forEach { outerItem ->
  innerList.forEach { innerItem ->
    if (outerItem.blah()) {
      set.put(outerItem)
      if (innerItem.foo()) { return "something" }
    }

[Colton Idle]

so my inner if's could also be improved.

not sure how honestly

[Landry Norris]

This loop looks interesting. Can the outer item if be moved outside of the inner for loop? That prevents inserting it to the set for every inner item (it's a set so no duplicates, but still). It's hard to tell from an abstract view like this, but it almost doesn't seem like what you need here is a 'for each combination'. I'm making some assumptions like that blah is stateless or that set is indeed a set and not a list.

[Colton Idle]

yeah. its kinda annoying. but as far as i can see it has to stay this way.

[Landry Norris]

Are the outer item and inner item related in any way such that you can flatten this to a single list. It seems like what you care about is inner items that match a condition foo (specifically the first) when outer items match a condition blah. I don't see any clear relationship between them here in this code, though. Can the set just be outerList.filter { it.blah() } and the return value be innerList.first { it.foo() }? Unless there's a relationship between them that was omitted for brevity, you may not need the nested loop.

[Landry Norris]

I remember seeing something in the advent of code videos. I believe my solution was to make a 'forEachCombination(list1: List<T>, list2: List<R>, block: (T, R) -> Unit)'. You could reduce this to 3 layers by using that. It's basically just a function that does the two for loops and calls block. The Jetbrains video did something similar, but more elegant if I remember correctly.

[Jacob]

for(outerItem in outerList.filter{it.blah()}){}

[Klitos Kyriacou]

Sam's suggestion:
outerList.asSequence().flatMap { innerList.asSequence() }.forEach { ... }
unfortunately just produces outerList.size copies of innerList items. To get the actual Cartesian product, you need something like this:

outerList.asSequence().flatMap { outer ->
    innerList.asSequence().map { inner ->
        outer to inner
    }
}
    .forEach { (outer, inner) ->
        ... 
    }

which unfortunately doesn't save you any indent depth.

[ephemient]

how about this? scales to any number of lists, as long as the block is idempotent before all items are chosen

chooseAll {
    val x = choose(0, 3, 6)
    val y = choose(0, 1, 2)
    println("$x + $y = ${x + y}")
}

0 + 0 = 0
0 + 1 = 1
0 + 2 = 2
3 + 0 = 3
3 + 1 = 4
3 + 2 = 5
6 + 0 = 6
6 + 1 = 7
6 + 2 = 8

Untitled.kt

[ephemient]

(inspired by wanting to be able to use something like Haskell's

sequence_ $ do
    x <- [0, 3, 6]
    y <- [0, 1, 2]
    pure $ printf "%d + %d = %d\n" x y (x + y)

in Kotlin… unfortunately can't statically guarantee the lack of side-effects in Kotlin, unlike Haskell)

[ephemient]

actually I forgot about the fact that Scala has it built-in,

for {
    x <- 0 to 6 by 3
    y <- 0 to 2
} println(s"$x + $y = ${x + y}")

I wonder if anyone has proposed adding similar to Kotlin

[Riccardo Lippolis]

https://youtrack.jetbrains.com/issue/KT-18861/Is-there-possibility-that-kotlin-could-support-for-comprehensions#focus=Comments-27-5583310.0-0