# distance(from:to:) Returns the distance between two indices. ``` func distance(from start: AnyBidirectionalCollection.Index, to end: AnyBidirectionalCollection.Index) -> Int ``` ## Parameters `start` A valid index of the collection. `end` Another valid index of the collection. If `end` is equal to `start`, the result is zero. ## Return Value The distance between `start` and `end`. The result can be negative only if the collection conforms to the `BidirectionalCollection` protocol. ## Discussion Unless the collection conforms to the `BidirectionalCollection` protocol, `start` must be less than or equal to `end`. > Complexity: O(1) if the collection conforms to > `RandomAccessCollection`; otherwise, O(*k*), where *k* is the > resulting distance. --- 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)