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Title
h

Hullaballoonatic

08/31/2018, 4:19 PM
i've been creating classes every time. i'll look into destructive declarations, thanks!
a

adam-mcneilly

08/31/2018, 4:20 PM
You'd still need to create a data class to be returned by the function, but then you can easily destructure at the call site. The docs linked have a good example of this.
h

Hullaballoonatic

08/31/2018, 4:21 PM
yeah, this is awesome. i learned about two kotlin features today, and i'm all giddy
❤️ 1
s

Shawn

08/31/2018, 4:22 PM
Or, I mean,
Pair
or
Triple
can do in a pinch
2
h

Hullaballoonatic

08/31/2018, 4:22 PM
yeah, i love pair
a

adam-mcneilly

08/31/2018, 4:22 PM
You can also destructure a pair!
So if you want to use it as the return type on your function, you can still use destructuring at the call site. 🙂
h

Hullaballoonatic

08/31/2018, 4:23 PM
you mean like it.first and it.second?
a

adam-mcneilly

08/31/2018, 4:23 PM
fun foo(): Pair<Int, Int> { }

val (x, y) = foo()
s

Shawn

08/31/2018, 4:23 PM
@potter ^
might be relevant to what you’re asking for
unless you want named accessors, in which case you’ll need an inline
object { ... }
expression
p

potter

08/31/2018, 4:25 PM
oh yeah, I forgot about those. still not a general solution (4+ returns), but covers most of my use cases
a

adam-mcneilly

08/31/2018, 4:25 PM
You can destructure a
List<T>
up to 5 items. Any more than that, and you'd need a data class. I'd also argue that any more than that means you might want to question if destructuring is the most readable solution (you may say yes, but worth questioning after a point).
👍 1
h

Hullaballoonatic

08/31/2018, 4:26 PM
yeah
if someone is returning like 8 distinct values from a fn then it is doing way more than it should
p

potter

08/31/2018, 4:27 PM
yeah, makes sense
a

adam-mcneilly

08/31/2018, 4:28 PM
Definitely. And if not that, then it means those 8 values are actually connected in some way, which leads me to believe they're better off as a data class because they represent something larger than the individual values.
👍 1
Knowing that you can destructure a list is really nice, because I think a good example use case is coordinates. This is my favorite example for showing off destructuring:
val (x, y, z) = arrayOf(5, 10, 5)
Or, looping through a map by destructuring the entry class:
for ((key, value) in map) { }
h

Hullaballoonatic

08/31/2018, 4:31 PM
haha, i am literally working with coordinates right now
a

adam-mcneilly

08/31/2018, 4:31 PM
😎 nailed it
p

potter

08/31/2018, 4:32 PM
for the list, all of the returned values have to have the same type, right? otherwise type inference won't work?
a

adam-mcneilly

08/31/2018, 4:33 PM
For the list I believe that's true. Whatever
<T>
is for you list, that's what you have to destructure to.
As far as I'm aware. I would have to test that out.
h

Hullaballoonatic

08/31/2018, 4:34 PM
so if i'm rolling through an array that stores x1y1x2y2x3y3.... is there a nicer way to iterate through them than
val arr = arrayOf(0,0,1,3,4,2....)
for (i in arr.indices step 2) {
  arr[i]++
  arr[i+1]++
}
using destructuring?
p

potter

08/31/2018, 4:36 PM
could whatever generates them generate a
Pair<x,y>
instead?
a

adam-mcneilly

08/31/2018, 4:36 PM
There is something like that.
windowed
I believe. But let me back up - why have an array of x1y1x2y2... and not a list of pairs?
s

Shawn

08/31/2018, 4:37 PM
or
chunked
, depending on your use case
h

Hullaballoonatic

08/31/2018, 4:37 PM
well, yeah, I could do
List<Pair<Int,Int>>
but I'm doing breadth first search and wanna be really efficient with memory
so i'm using a bytearray
a

adam-mcneilly

08/31/2018, 4:37 PM
hmm
h

Hullaballoonatic

08/31/2018, 4:38 PM
i've never used chunked either
a

adam-mcneilly

08/31/2018, 4:38 PM
chunked
is nice
if you have your coordinates in the byte array you mentioned, you can use
chunked
to get the
List<Pair>
and then search through that. I guess the performance hit is that you go through the list twice - one to prettify it, one to handle the coordinates I would think - hard to know your exact use case.
h

Hullaballoonatic

08/31/2018, 4:40 PM
i have trouble with collections in kotlin. generating alterations on a base set of coordinates required some funkiness like this:
val children: List<ByteArray>
        get() {
            val result = ArrayList<ByteArray>()
            val original = positions.toList().toImmutableList()
            original.forEachIndexed { i, byte ->
                result += original.set(i, (byte + 1).b).toByteArray()
                result += original.set(i, (byte - 1).b).toByteArray()
            }
            return result
        }
this is AI stuff, or i'm throttled by memory, not cpu
a

adam-mcneilly

08/31/2018, 4:41 PM
Hmm let me tinker for a sec
p

potter

08/31/2018, 4:41 PM
doesn't kotlin have lazy operations (like java8 streams) that let you prettify and consume in one iteration?
h

Hullaballoonatic

08/31/2018, 4:41 PM
i don't care how long it takes for the operation to run 😛
p

potter

08/31/2018, 4:41 PM
I forget what they're called
h

Hullaballoonatic

08/31/2018, 4:41 PM
delegates
i've only ever used them for observables
a

adam-mcneilly

08/31/2018, 4:41 PM
Casey - can you give me an example of an input array, and what you'd expect as the output, and I can tinker to see if there's a more idiomatic way to pull it off?
h

Hullaballoonatic

08/31/2018, 4:42 PM
it's not a large program if you want me to just hand it all over for context
h

Hullaballoonatic

08/31/2018, 4:42 PM
it's not working correctly atm
though...
a

adam-mcneilly

08/31/2018, 4:42 PM
hmm
one sec
I think I see what this is trying to do
p

potter

08/31/2018, 4:46 PM
fun main(args: Array<String>) {
    listOf(1, 1, 2, 2, 3, 3)
        .asSequence()
        .chunked(2) { Pair(it[0], it[1]) }
        .map { println("${it.first},${it.second}") }
        .toList()
}
that prints this:
1,1
2,2
3,3
obviously replace the println with an actual mapping
h

Hullaballoonatic

08/31/2018, 4:47 PM
alright. slick!
p

potter

08/31/2018, 4:48 PM
but only one
Pair
reference is held at a time, so it doesn't require a lot of memory (it'll create garbage, though)
a

adam-mcneilly

08/31/2018, 4:48 PM
yeah I think that's what you're looking for
h

Hullaballoonatic

08/31/2018, 5:40 PM
i also like to write
Pair(it[0], it[1])
as
it[0] to it[1]
p

potter

08/31/2018, 7:40 PM
oh yeah, good call