# BidirectionalCollection Implementations ## Topics ### Instance Properties [`var last: Self.Element?`](/documentation/Swift/Substring/last) The last element of the collection. ### Instance Methods [`func difference(from: C) -> CollectionDifference`](/documentation/Swift/Substring/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/Substring/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: Substring.Index, to: Substring.Index) -> Int`](/documentation/Swift/Substring/distance(from:to:)) Returns the distance between two indices. [`func dropLast(Int) -> Self.SubSequence`](/documentation/Swift/Substring/dropLast(_:)) Returns a subsequence containing all but the specified number of final elements. [`func formIndex(before: inout Self.Index)`](/documentation/Swift/Substring/formIndex(before:)) Replaces the given index with its predecessor. [`func index(Substring.Index, offsetBy: Int) -> Substring.Index`](/documentation/Swift/Substring/index(_:offsetBy:)) Returns an index that is the specified distance from the given index. [`func index(Substring.Index, offsetBy: Int, limitedBy: Substring.Index) -> Substring.Index?`](/documentation/Swift/Substring/index(_:offsetBy:limitedBy:)) Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index. [`func index(after: Substring.Index) -> Substring.Index`](/documentation/Swift/Substring/index(after:)) Returns the position immediately after the given index. [`func index(before: Substring.Index) -> Substring.Index`](/documentation/Swift/Substring/index(before:)) Returns the position immediately before the given index. [`func last(where: (Self.Element) throws -> Bool) rethrows -> Self.Element?`](/documentation/Swift/Substring/last(where:)) Returns the last element of the sequence that satisfies the given predicate. [`func lastIndex(of: Self.Element) -> Self.Index?`](/documentation/Swift/Substring/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/Substring/lastIndex(where:)) Returns the index of the last element in the collection that matches the given predicate. [`func popLast() -> Self.Element?`](/documentation/Swift/Substring/popLast()-7k3s0) Removes and returns the last element of the collection. [`func removeLast() -> Self.Element`](/documentation/Swift/Substring/removeLast()-2gcne) Removes and returns the last element of the collection. [`func removeLast(Int)`](/documentation/Swift/Substring/removeLast(_:)-8r1d9) Removes the given number of elements from the end of the collection. [`func reversed() -> ReversedCollection`](/documentation/Swift/Substring/reversed()) Returns a view presenting the elements of the collection in reverse order. [`func suffix(Int) -> Self.SubSequence`](/documentation/Swift/Substring/suffix(_:)) Returns a subsequence, up to the given maximum length, containing the final elements of the collection. ### Subscripts [`subscript(Range) -> Substring`](/documentation/Swift/Substring/subscript(_:)-6e3qj) Accesses a contiguous subrange of the collection’s elements. --- 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)