Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

Sets

Lists, as you have seen, allow duplicate elements (and are ordered, so duplicates – and other elements – can be identified by their position). But sometimes you want a collection that guarantees that its items are unique. For that, you use a Set.

Sets are like Lists in many ways. They use the same iteration functions, and Set also comes in read-only and mutable flavors.

But there are two major differences between lists and sets: The elements of a set are unique, and sets are not index-based, because the items in a set are not guaranteed to be in any particular order. (That said, you can still read an element at a particular index, which we will discuss shortly.)

Creating a set

Just as you create a list using the ...