I want to loop over the elements of a queue, and remove them in the process. is there a fancy way to...

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[LastExceed]

I want to loop over the elements of a queue, and remove them in the process. is there a fancy way to achieve this with for (x in y) or do i have to remove them manually ?

[David Eriksson]

You probably don't want to modify a list you are iterating 🙂

[LastExceed]

why not ?

[David Eriksson]

I was thinking of things like this: https://stackoverflow.com/questions/1196586/calling-remove-in-foreach-loop-in-java

[diesieben07]

val collection = mutableListOf(1, 2, 3)
val iterator = collection.iterator()
for (element in iterator) {
    if (element % 2 == 0) {
        iterator.remove()
    }
}

[FranSoto]

to avoid collateral damage, if other function is reading or working with that list, you are going to have inconsistencies

[LastExceed]

@FranSoto that's because of mutability in general, not mutating while iterating specifically

[David Eriksson]

I just invented a queue interface here but is this too manual? 🙂

while (!queue.isEmpty()) {
val item = queue.pop();
// do stufff
}

[LastExceed]

its not that bad, it just seemed like a code smell. usually there is fancy ways to achieve stuff like this, but guess not this time

[LastExceed]

right now i am using

for (element in collection) {
    collection.remove()
    //do sth
}

but it seems fishy somehow

[David Eriksson]

Looks like SO issue I linked to

[LastExceed]

well then it would be

val iterator = collection.iterator()
for (element in iterator) {
    iterator.remove()
    //do sth
}

i still get the impression that there's gotta be a better way to do this

[FranSoto]

if you need to remove each element before to proccess it, it's ok. Shouldn't be fancy

[cristiangm]

Why don't you use something like mapNotNull to create a new list without the items you don't want, or simply filter if you don't need to change any of them?

[Jakub Pi]

If this was Java, I'd use a ConcurrentLinkedQueue and repeatedly call poll() inside a while loop. In Kotlin, I'd avoid the use of mutable collections. Depends on the usecase.

[LastExceed]

I have a queue of user input parameters. I want to parse them 1 by 1 until a parameter matches a certain condition, at which point i will break out of the loop

[Derek Peirce]

You could make a custom Iterable.removingForEach { ... } extension method that does this. I don't believe any existing stdlib method will accomplish this. Java 8 has removeIf, but it won't be inlined, and you don't need the extra conditional evaluation of removeIf { true }

[diesieben07]

removeIf also has no guarantees about visiting each element only once and no guarantees about visiting them in order. The predicate you give it should be a pure function

[Jakub Pi]

Ok the queue was throwing me off, just use dropWhile() and pass it the inverse of your condition.

[Derek Peirce]

dropWhile will not modify the original queue, it will create a new list containing the elements that were not removed.