# BidirectionalCollection Implementations ## Topics ### Instance Properties [`var last: Self.Element?`](/documentation/Swift/Slice/last) The last element of the collection. ### Instance Methods [`func difference(from: C) -> CollectionDifference`](/documentation/Swift/Slice/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/Slice/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 formIndex(before: inout Slice.Index)`](/documentation/Swift/Slice/formIndex(before:)) Replaces the given index with its predecessor. [`func formIndex(before: inout Self.Index)`](/documentation/Swift/Slice/formIndex(before:)-d9pr) Replaces the given index with its predecessor. [`func index(before: Slice.Index) -> Slice.Index`](/documentation/Swift/Slice/index(before:)) Returns the position immediately before the given index. [`func joined(separator: String) -> String`](/documentation/Swift/Slice/joined(separator:)-6sxlg) 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/Slice/last(where:)) Returns the last element of the sequence that satisfies the given predicate. [`func lastIndex(of: Self.Element) -> Self.Index?`](/documentation/Swift/Slice/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/Slice/lastIndex(where:)) Returns the index of the last element in the collection that matches the given predicate. [`func popLast() -> Self.Element?`](/documentation/Swift/Slice/popLast()-7zlp7) Removes and returns the last element of the collection. [`func removeLast() -> Self.Element`](/documentation/Swift/Slice/removeLast()-29ty4) Removes and returns the last element of the collection. [`func removeLast(Int)`](/documentation/Swift/Slice/removeLast(_:)-4ijd6) Removes the given number of elements from the end of the collection. --- 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)