# Collection Implementations ## Topics ### Instance Properties [`var count: Int`](/documentation/Swift/LazySequence/count) Returns the number of elements. [`var count: Int`](/documentation/Swift/LazySequence/count-1cggd) The number of elements in the collection. [`var endIndex: LazySequence.Index`](/documentation/Swift/LazySequence/endIndex) The collection’s “past the end” position—that is, the position one greater than the last valid subscript argument. [`var indices: LazySequence.Indices`](/documentation/Swift/LazySequence/indices-swift.property) The indices that are valid for subscripting the collection, in ascending order. [`var isEmpty: Bool`](/documentation/Swift/LazySequence/isEmpty) A Boolean value indicating whether the collection is empty. [`var isEmpty: Bool`](/documentation/Swift/LazySequence/isEmpty-1upms) A Boolean value indicating whether the collection is empty. [`var startIndex: LazySequence.Index`](/documentation/Swift/LazySequence/startIndex) The position of the first element in a non-empty collection. ### Instance Methods [`func distance(from: LazySequence.Index, to: LazySequence.Index) -> Int`](/documentation/Swift/LazySequence/distance(from:to:)) Returns the distance between two indices. [`func distance(from: Self.Index, to: Self.Index) -> Int`](/documentation/Swift/LazySequence/distance(from:to:)-396sb) Returns the distance between two indices. [`func firstIndex(of: Self.Element) -> Self.Index?`](/documentation/Swift/LazySequence/firstIndex(of:)) Returns the first index where the specified value appears in the collection. [`func firstIndex(where: (Self.Element) throws -> Bool) rethrows -> Self.Index?`](/documentation/Swift/LazySequence/firstIndex(where:)) Returns the first index in which an element of the collection satisfies the given predicate. [`func formIndex(inout Self.Index, offsetBy: Int)`](/documentation/Swift/LazySequence/formIndex(_:offsetBy:)) Offsets the given index by the specified distance. [`func formIndex(inout Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Bool`](/documentation/Swift/LazySequence/formIndex(_:offsetBy:limitedBy:)) Offsets the given index by the specified distance, or so that it equals the given limiting index. [`func formIndex(after: inout Self.Index)`](/documentation/Swift/LazySequence/formIndex(after:)) Replaces the given index with its successor. [`func index(LazySequence.Index, offsetBy: Int) -> LazySequence.Index`](/documentation/Swift/LazySequence/index(_:offsetBy:)) Returns an index that is the specified distance from the given index. [`func index(Self.Index, offsetBy: Int) -> Self.Index`](/documentation/Swift/LazySequence/index(_:offsetBy:)-t8sl) Returns an index that is the specified distance from the given index. [`func index(LazySequence.Index, offsetBy: Int, limitedBy: LazySequence.Index) -> LazySequence.Index?`](/documentation/Swift/LazySequence/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(Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Self.Index?`](/documentation/Swift/LazySequence/index(_:offsetBy:limitedBy:)-62vws) Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index. [`func index(after: LazySequence.Index) -> LazySequence.Index`](/documentation/Swift/LazySequence/index(after:)) Returns the position immediately after the given index. [`func index(of: Self.Element) -> Self.Index?`](/documentation/Swift/LazySequence/index(of:)) Returns the first index where the specified value appears in the collection. [`func indices(of: Self.Element) -> RangeSet`](/documentation/Swift/LazySequence/indices(of:)) Returns the indices of all the elements that are equal to the given element. [`func indices(where: (Self.Element) throws -> Bool) rethrows -> RangeSet`](/documentation/Swift/LazySequence/indices(where:)) Returns the indices of all the elements that match the given predicate. [`func makeIterator() -> LazySequence.Iterator`](/documentation/Swift/LazySequence/makeIterator()) Returns an iterator over the elements of the collection. [`func map((Self.Element) throws(E) -> T) throws(E) -> [T]`](/documentation/Swift/LazySequence/map(_:)-7wx5z) Returns an array containing the results of mapping the given closure over the sequence’s elements. [`func prefix(through: Self.Index) -> Self.SubSequence`](/documentation/Swift/LazySequence/prefix(through:)) Returns a subsequence from the start of the collection through the specified position. [`func prefix(upTo: Self.Index) -> Self.SubSequence`](/documentation/Swift/LazySequence/prefix(upTo:)) Returns a subsequence from the start of the collection up to, but not including, the specified position. [`func randomElement() -> Self.Element?`](/documentation/Swift/LazySequence/randomElement()) Returns a random element of the collection. [`func randomElement(using: inout T) -> Self.Element?`](/documentation/Swift/LazySequence/randomElement(using:)) Returns a random element of the collection, using the given generator as a source for randomness. [`func removingSubranges(RangeSet) -> DiscontiguousSlice`](/documentation/Swift/LazySequence/removingSubranges(_:)) Returns a collection of the elements in this collection that are not represented by the given range set. [`func split(separator: Self.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Self.SubSequence]`](/documentation/Swift/LazySequence/split(separator:maxSplits:omittingEmptySubsequences:)-ki1c) Returns the longest possible subsequences of the collection, in order, around elements equal to the given element. [`func suffix(from: Self.Index) -> Self.SubSequence`](/documentation/Swift/LazySequence/suffix(from:)) Returns a subsequence from the specified position to the end of the collection. ### Subscripts [`subscript(LazySequence.Index) -> LazySequence.Element`](/documentation/Swift/LazySequence/subscript(_:)) Accesses the element at `position`. [`subscript(RangeSet) -> DiscontiguousSlice`](/documentation/Swift/LazySequence/subscript(_:)-1iwxl) Accesses a view of this collection with the elements at the given indices. [`subscript(UnboundedRange) -> Self.SubSequence`](/documentation/Swift/LazySequence/subscript(_:)-1rlj) [`subscript(Range) -> Slice`](/documentation/Swift/LazySequence/subscript(_:)-8iflg) Accesses a contiguous subrange of the collection’s elements. [`subscript(R) -> Self.SubSequence`](/documentation/Swift/LazySequence/subscript(_:)-9kt1v) Accesses the contiguous subrange of the collection’s elements specified by a range expression. ### Type Aliases [`typealias Index`](/documentation/Swift/LazySequence/Index) A type that represents a valid position in the collection. [`typealias Indices`](/documentation/Swift/LazySequence/Indices-swift.typealias) A type that represents the indices that are valid for subscripting the collection, in ascending order. [`typealias Iterator`](/documentation/Swift/LazySequence/Iterator) A type that provides the collection’s iteration interface and encapsulates its iteration state. [`typealias SubSequence`](/documentation/Swift/LazySequence/SubSequence) A collection representing a contiguous subrange of this collection’s elements. The subsequence shares indices with the original 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)