# UnboundedRange_ A range expression that represents the entire range of a collection. ``` @frozen enum UnboundedRange_ ``` ## Overview You can use the unbounded range operator (`...`) to create a slice of a collection that contains all of the collection’s elements. Slicing with an unbounded range is essentially a conversion of a collection instance into its slice type. For example, the following code declares `countLetterChanges(_:_:)`, a function that finds the number of changes required to change one word or phrase into another. The function uses a recursive approach to perform the same comparisons on smaller and smaller pieces of the original strings. In order to use recursion without making copies of the strings at each step, `countLetterChanges(_:_:)` uses `Substring`, a string’s slice type, for its parameters. ``` func countLetterChanges(_ s1: Substring, _ s2: Substring) -> Int { if s1.isEmpty { return s2.count } if s2.isEmpty { return s1.count } let cost = s1.first == s2.first ? 0 : 1 return min( countLetterChanges(s1.dropFirst(), s2) + 1, countLetterChanges(s1, s2.dropFirst()) + 1, countLetterChanges(s1.dropFirst(), s2.dropFirst()) + cost) } ``` To call `countLetterChanges(_:_:)` with two strings, use an unbounded range in each string’s subscript. ``` let word1 = "grizzly" let word2 = "grisly" let changes = countLetterChanges(word1[...], word2[...]) // changes == 2 ``` ## Topics ### Creating an Unbounded Range [`...(_:)`](/documentation/Swift/UnboundedRange_/...(_:)) Creates an unbounded range expression. [`UnboundedRange`](/documentation/Swift/UnboundedRange) The type of an unbounded range operator. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)