I have already checked, but just to be sure, allow me to ask: is there an immutable deque in Kotlin....

# getting-started

[Xad Kile]

I have already checked, but just to be sure, allow me to ask: is there an immutable deque in Kotlin. There's ArrayDeque but it is not immutable. I am using LinkedBlockingDeque (a java implementation), but want to replace it with an immutable one.

[Sam]

Given that the point of using a specialised queue implementation (over, say, a regular ArrayList) is efficient enqueue and dequeue operations (i.e. mutations), would there be much point to an immutable deque? Could you just use an immutable list?

[Xad Kile]

@Sam You're right, I'll just use the immutable list. Thanks

[Klitos Kyriacou]

I've just looked through documentation and got confused. In Kotlin, ArrayDeque implements MutableList (and therefore also List). But in Java, ArrayDeque implements Deque and Queue but not List.

That sounds like a problem if a Java method calls a method that it expects to return a List. If the called method is written in Kotlin, it can return an ArrayDeque (because that's a List in Kotlin) but when Java gets it, it won't be a Java List.

[Sam]

@Klitos Kyriacou that’s okay because the Java ArrayDeque and the Kotlin ArrayDeque are actually two separate classes. They’re not aliases for one another like ArrayList would be.

[Xad Kile]

@Klitos Kyriacou The java ArrayDeque is identified as "java.util.ArrayDeque", while the kotlin one is "kotlin.collection.ArrayDeque", so there shouldn't be any error

[ephemient]

I can see where the confusion may come from, given that kotlin.collections.ArrayList == java.util.ArrayList etc., but there's only a limited number of types for which that aliasing takes place

[Jacob]

and kotlin ArrayDeque is a fairly recent addition. If you're working toy problems in hacckerrank or leetcode its not going to be available

[ephemient]

since 1.4, released August 2020. I don't think that's very recent by Kotlin standards; hackerrank and leetcode are just outrageously outdated

[Michael de Kaste]

codewars also works with old stuff for kotlin which constantly annoys me