# BidirectionalCollection Implementations ## Topics ### Instance Properties [`var last: Self.Element?`](/documentation/Swift/LazySequence/last) The last element of the collection. ### Instance Methods [`func difference(from: C) -> CollectionDifference`](/documentation/Swift/LazySequence/difference(from:)) Returns the difference needed to produce this collection’s ordered elements from the given collection. [`func difference(from: C, by: (C.Element, Self.Element) -> Bool) -> CollectionDifference`](/documentation/Swift/LazySequence/difference(from:by:)) Returns the difference needed to produce this collection’s ordered elements from the given collection, using the given predicate as an equivalence test. [`func distance(from: Self.Index, to: Self.Index) -> Int`](/documentation/Swift/LazySequence/distance(from:to:)-5ong5) [`func formIndex(before: inout Self.Index)`](/documentation/Swift/LazySequence/formIndex(before:)) Replaces the given index with its predecessor. [`func index(Self.Index, offsetBy: Int) -> Self.Index`](/documentation/Swift/LazySequence/index(_:offsetBy:)-9c2fj) [`func index(Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Self.Index?`](/documentation/Swift/LazySequence/index(_:offsetBy:limitedBy:)-9juzm) [`func index(before: LazySequence.Index) -> LazySequence.Index`](/documentation/Swift/LazySequence/index(before:)) Returns the position immediately before the given index. [`func joined(separator: String) -> String`](/documentation/Swift/LazySequence/joined(separator:)-5e92i) Returns a new string by concatenating the elements of the sequence, adding the given separator between each element. [`func last(where: (Self.Element) throws -> Bool) rethrows -> Self.Element?`](/documentation/Swift/LazySequence/last(where:)) Returns the last element of the sequence that satisfies the given predicate. [`func lastIndex(of: Self.Element) -> Self.Index?`](/documentation/Swift/LazySequence/lastIndex(of:)) Returns the last index where the specified value appears in the collection. [`func lastIndex(where: (Self.Element) throws -> Bool) rethrows -> Self.Index?`](/documentation/Swift/LazySequence/lastIndex(where:)) Returns the index of the last element in the collection that matches the given predicate. --- 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)