That is, 1 and 5 are also included and the step value is 1. For example, a range of 1.5 means 1,2,3,4,5.

By default, the values are inclusive for the given range. The lambda is inlined so likely there is no real difference in performance. A Kotlin range can also be created by using the rangeTo () and downTo () function as well. NOTE: the helper functions use flatMap() since there is no flatten() method or extension for Array which is the type received from the vararg. and the usage for those helpers: val validLetters = sparseListOf('a'.'z', 'A'.'Z') In Kotlin people typically create a helper function to wrap things like this up nicely if you happen to re-use this code a lot: // helper functionsįun sparseListOf(vararg ranges: CharRange): List = ranges.flatMap Or go more lazy as a Sequence (not sure it matters here at all to be lazier): sequenceOf('a'.'z','A'.'Z').flatten() Each + will make a copy of the list: val validLetters = ('a'.'z') + ('A'.'Z') Or a shorter form (from is to use the plus() + operator of Iterable ( an interface that ranges implement). The difference is, if we use a sequence to process a collection. Like Stream s in Java, Sequence s in Kotlin execute lazily. It’s also an interface, including intermediate operations like map () and filter (), as well as terminal operations like count () and find ().

You can go slightly shorter for a list by using flatten() instead of flatMap(): listOf('a'.'z','A'.'Z').flatten() A sequence is a container Sequence with type T.

Kotlin range step