Generic Structure

Slice

A view into a subsequence of elements of another collection.

Declaration

@frozen struct Slice<Base> where Base : Collection

Overview

A slice stores a base collection and the start and end indices of the view. It does not copy the elements from the collection into separate storage. Thus, creating a slice has O(1) complexity.

Slices Share Indices

Indices of a slice can be used interchangeably with indices of the base collection. An element of a slice is located under the same index in the slice and in the base collection, as long as neither the collection nor the slice has been mutated since the slice was created.

For example, suppose you have an array holding the number of absences from each class during a session.

var absences = [0, 2, 0, 4, 0, 3, 1, 0]

You’re tasked with finding the day with the most absences in the second half of the session. To find the index of the day in question, follow these setps:

  1. Create a slice of the absences array that holds the second half of the days.

  2. Use the max(by:) method to determine the index of the day with the most absences.

  3. Print the result using the index found in step 2 on the original absences array.

Here’s an implementation of those steps:

let secondHalf = absences.suffix(absences.count / 2)
if let i = secondHalf.indices.max(by: { secondHalf[$0] < secondHalf[$1] }) {
    print("Highest second-half absences: \(absences[i])")
}
// Prints "Highest second-half absences: 3"

Slices Inherit Semantics

A slice inherits the value or reference semantics of its base collection. That is, if a Slice instance is wrapped around a mutable collection that has value semantics, such as an array, mutating the original collection would trigger a copy of that collection, and not affect the base collection stored inside of the slice.

For example, if you update the last element of the absences array from 0 to 2, the secondHalf slice is unchanged.

absences[7] = 2
print(absences)
// Prints "[0, 2, 0, 4, 0, 3, 1, 2]"
print(secondHalf)
// Prints "[0, 3, 1, 0]"

Use slices only for transient computation. A slice may hold a reference to the entire storage of a larger collection, not just to the portion it presents, even after the base collection’s lifetime ends. Long-term storage of a slice may therefore prolong the lifetime of elements that are no longer otherwise accessible, which can erroneously appear to be memory leakage.

Topics

Type Aliases

typealias Slice.Element

A type representing the sequence’s elements.

typealias Slice.Index

A type that represents a position in the collection.

typealias Slice.Indices

A type that represents the indices that are valid for subscripting the collection, in ascending order.

typealias Slice.Iterator

A type that provides the collection’s iteration interface and encapsulates its iteration state.

typealias Slice.Elements

A Sequence that can contain the same elements as this one, possibly with a simpler type.

Beta
typealias Slice.Regions
typealias Slice.SubSequence

A sequence that represents a contiguous subrange of the collection’s elements.

Initializers

init()

Creates a new, empty collection.

init<S>(S)

Creates a new instance of a collection containing the elements of a sequence.

init<S>(S)

Creates a new instance of a collection containing the elements of a sequence.

init(base: Base, bounds: Range<Base.Index>)

Creates a view into the given collection that allows access to elements within the specified range.

init(repeating: Base.Element, count: Int)

Creates a new collection containing the specified number of a single, repeated value.

init(repeating: Base.Element, count: Int)

Creates a new collection containing the specified number of a single, repeated value.

Instance Properties

var base: Base

The underlying collection of the slice.

var count: Int

The number of elements in the collection.

var elements: Slice<Base>

Identical to self.

var endIndex: Base.Index

The collection’s “past the end” position—that is, the position one greater than the last valid subscript argument.

var first: Base.Element?

The first element of the collection.

var indices: DefaultIndices<Slice<Base>>

The indices that are valid for subscripting the collection, in ascending order.

var indices: Base.Indices

The indices that are valid for subscripting the collection, in ascending order.

var indices: Range<Base.Index>

The indices that are valid for subscripting the collection, in ascending order.

var isEmpty: Bool

A Boolean value indicating whether the collection is empty.

var last: Base.Element?

The last element of the collection.

var regions: [Base.Regions.Element.SubSequence]
var startIndex: Base.Index

The position of the first element in a nonempty collection.

var underestimatedCount: Int

A value less than or equal to the number of elements in the collection.

Instance Methods

func allSatisfy((Base.Element) -> Bool) -> Bool

Returns a Boolean value indicating whether every element of a sequence satisfies a given predicate.

func append(Base.Element)

Adds an element to the end of the collection.

func append<S>(contentsOf: S)

Adds the elements of a sequence or collection to the end of this collection.

func applying(CollectionDifference<Base.Element>) -> Slice<Base>?

Applies the given difference to this collection.

Beta
func compactMap<ElementOfResult>((Base.Element) -> ElementOfResult?) -> [ElementOfResult]

Returns an array containing the non-nil results of calling the given transformation with each element of this sequence.

func contains(Base.Element) -> Bool

Returns a Boolean value indicating whether the sequence contains the given element.

func contains(where: (Base.Element) -> Bool) -> Bool

Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.

func difference<C>(from: C) -> CollectionDifference<Base.Element>

Returns the difference needed to produce this collection’s ordered elements from the given collection.

Beta
func difference<C>(from: C, by: (C.Element, Base.Element) -> Bool) -> CollectionDifference<Base.Element>

Returns the difference needed to produce this collection’s ordered elements from the given collection, using the given predicate as an equivalence test.

Beta
func drop(while: (Base.Element) -> Bool) -> Slice<Base>

Returns a subsequence by skipping elements while predicate returns true and returning the remaining elements.

func dropFirst(Int) -> Slice<Base>

Returns a subsequence containing all but the given number of initial elements.

func dropLast(Int) -> Slice<Base>

Returns a subsequence containing all but the specified number of final elements.

func elementsEqual<OtherSequence>(OtherSequence) -> Bool

Returns a Boolean value indicating whether this sequence and another sequence contain the same elements in the same order.

func elementsEqual<OtherSequence>(OtherSequence, by: (Base.Element, OtherSequence.Element) -> Bool) -> Bool

Returns a Boolean value indicating whether this sequence and another sequence contain equivalent elements in the same order, using the given predicate as the equivalence test.

func enumerated() -> EnumeratedSequence<Slice<Base>>

Returns a sequence of pairs (n, x), where n represents a consecutive integer starting at zero and x represents an element of the sequence.

func filter((Base.Element) -> Bool) -> [Base.Element]

Returns an array containing, in order, the elements of the sequence that satisfy the given predicate.

func first(where: (Base.Element) -> Bool) -> Base.Element?

Returns the first element of the sequence that satisfies the given predicate.

func firstIndex(of: Base.Element) -> Base.Index?

Returns the first index where the specified value appears in the collection.

func firstIndex(where: (Base.Element) -> Bool) -> Base.Index?

Returns the first index in which an element of the collection satisfies the given predicate.

func flatMap<SegmentOfResult>((Base.Element) -> SegmentOfResult) -> [SegmentOfResult.Element]

Returns an array containing the concatenated results of calling the given transformation with each element of this sequence.

func forEach((Base.Element) -> Void)

Calls the given closure on each element in the sequence in the same order as a for-in loop.

func formIndex(inout Base.Index, offsetBy: Int)

Offsets the given index by the specified distance.

func formIndex(inout Base.Index, offsetBy: Int, limitedBy: Base.Index) -> Bool

Offsets the given index by the specified distance, or so that it equals the given limiting index.

func formIndex(after: inout Slice<Base>.Index)

Replaces the given index with its successor.

func formIndex(before: inout Slice<Base>.Index)

Replaces the given index with its predecessor.

func index(Slice<Base>.Index, offsetBy: Int) -> Slice<Base>.Index

Returns an index that is the specified distance from the given index.

func index(Slice<Base>.Index, offsetBy: Int, limitedBy: Slice<Base>.Index) -> Slice<Base>.Index?

Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index.

func index(after: Slice<Base>.Index) -> Slice<Base>.Index

Returns the position immediately after the given index.

func index(before: Slice<Base>.Index) -> Slice<Base>.Index

Returns the position immediately before the given index.

func index(of: Base.Element) -> Base.Index?

Returns the first index where the specified value appears in the collection.

Deprecated
func insert(Base.Element, at: Slice<Base>.Index)
func insert(Base.Element, at: Slice<Base>.Index)

Inserts a new element into the collection at the specified position.

func insert(Base.Element, at: Base.Index)

Inserts a new element into the collection at the specified position.

func insert<S>(contentsOf: S, at: Slice<Base>.Index)

Inserts the elements of a sequence into the collection at the specified position.

func insert<S>(contentsOf: S, at: Slice<Base>.Index)
func insert<C>(contentsOf: C, at: Base.Index)

Inserts the elements of a sequence into the collection at the specified position.

func joined() -> FlattenSequence<Slice<Base>>

Returns the elements of this sequence of sequences, concatenated.

func joined() -> LazySequence<FlattenSequence<Slice<Base>>>

Returns a lazy sequence that concatenates the elements of this sequence of sequences.

func joined<Separator>(separator: Separator) -> JoinedSequence<Slice<Base>>

Returns the concatenated elements of this sequence of sequences, inserting the given separator between each element.

func joined(separator: String) -> String

Returns a new string by concatenating the elements of the sequence, adding the given separator between each element.

func joined(separator: String) -> String

Returns a new string by concatenating the elements of the sequence, adding the given separator between each element.

func last(where: (Base.Element) -> Bool) -> Base.Element?

Returns the last element of the sequence that satisfies the given predicate.

func lastIndex(of: Base.Element) -> Base.Index?

Returns the last index where the specified value appears in the collection.

func lastIndex(where: (Base.Element) -> Bool) -> Base.Index?

Returns the index of the last element in the collection that matches the given predicate.

func lexicographicallyPrecedes<OtherSequence>(OtherSequence) -> Bool

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the less-than operator (<) to compare elements.

func lexicographicallyPrecedes<OtherSequence>(OtherSequence, by: (Base.Element, Base.Element) -> Bool) -> Bool

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the given predicate to compare elements.

func makeIterator() -> IndexingIterator<Slice<Base>>

Returns an iterator over the elements of the collection.

func map<U>((Base.Element) -> U) -> LazyMapSequence<Slice<Base>, U>

Returns a LazyMapSequence over this Sequence. The elements of the result are computed lazily, each time they are read, by calling transform function on a base element.

func map<T>((Base.Element) -> T) -> [T]

Returns an array containing the results of mapping the given closure over the sequence’s elements.

func max() -> Base.Element?

Returns the maximum element in the sequence.

func max(by: (Base.Element, Base.Element) -> Bool) -> Base.Element?

Returns the maximum element in the sequence, using the given predicate as the comparison between elements.

func min() -> Base.Element?

Returns the minimum element in the sequence.

func min(by: (Base.Element, Base.Element) -> Bool) -> Base.Element?

Returns the minimum element in the sequence, using the given predicate as the comparison between elements.

func partition(by: (Base.Element) -> Bool) -> Base.Index

Reorders the elements of the collection such that all the elements that match the given predicate are after all the elements that don’t match.

func popFirst() -> Base.Element?

Removes and returns the first element of the collection.

func popLast() -> Base.Element?

Removes and returns the last element of the collection.

func prefix(Int) -> Slice<Base>

Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.

func prefix(through: Base.Index) -> Slice<Base>

Returns a subsequence from the start of the collection through the specified position.

func prefix(upTo: Base.Index) -> Slice<Base>

Returns a subsequence from the start of the collection up to, but not including, the specified position.

func prefix(while: (Base.Element) -> Bool) -> Slice<Base>

Returns a subsequence containing the initial elements until predicate returns false and skipping the remaining elements.

func randomElement() -> Base.Element?

Returns a random element of the collection.

func randomElement<T>(using: inout T) -> Base.Element?

Returns a random element of the collection, using the given generator as a source for randomness.

func reduce<Result>(Result, (Result, Base.Element) -> Result) -> Result

Returns the result of combining the elements of the sequence using the given closure.

func reduce<Result>(into: Result, (inout Result, Base.Element) -> ()) -> Result

Returns the result of combining the elements of the sequence using the given closure.

func remove(at: Base.Index) -> Base.Element

Removes and returns the element at the specified position.

func remove(at: Slice<Base>.Index) -> Base.Element
func remove(at: Slice<Base>.Index) -> Base.Element

Removes and returns the element at the specified position.

func removeAll(keepingCapacity: Bool)

Removes all elements from the collection.

func removeAll(where: (Base.Element) -> Bool)

Removes all the elements that satisfy the given predicate.

func removeFirst() -> Base.Element

Removes and returns the first element of the collection.

func removeFirst(Int)

Removes the specified number of elements from the beginning of the collection.

func removeLast() -> Base.Element

Removes and returns the last element of the collection.

func removeLast(Int)

Removes the specified number of elements from the end of the collection.

func removeSubrange<R>(R)

Removes the elements in the specified subrange from the collection.

func removeSubrange(Range<Base.Index>)

Removes the elements in the specified subrange from the collection.

func removeSubrange(Range<Slice<Base>.Index>)
func removeSubrange(Range<Slice<Base>.Index>)

Removes the specified subrange of elements from the collection.

func replaceSubrange<C>(Range<Slice<Base>.Index>, with: C)

Replaces the specified subrange of elements with the given collection.

func replaceSubrange<C>(Range<Slice<Base>.Index>, with: C)
func replaceSubrange<C, R>(R, with: C)

Replaces the specified subrange of elements with the given collection.

func reserveCapacity(Int)

Prepares the collection to store the specified number of elements, when doing so is appropriate for the underlying type.

func reverse()

Reverses the elements of the collection in place.

func reversed() -> [Base.Element]

Returns an array containing the elements of this sequence in reverse order.

func shuffle()

Shuffles the collection in place.

func shuffle<T>(using: inout T)

Shuffles the collection in place, using the given generator as a source for randomness.

func shuffled() -> [Base.Element]

Returns the elements of the sequence, shuffled.

func shuffled<T>(using: inout T) -> [Base.Element]

Returns the elements of the sequence, shuffled using the given generator as a source for randomness.

func sort()

Sorts the collection in place.

func sort(by: (Base.Element, Base.Element) -> Bool)

Sorts the collection in place, using the given predicate as the comparison between elements.

func sorted() -> [Base.Element]

Returns the elements of the sequence, sorted.

func sorted(by: (Base.Element, Base.Element) -> Bool) -> [Base.Element]

Returns the elements of the sequence, sorted using the given predicate as the comparison between elements.

func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (Base.Element) -> Bool) -> [Slice<Base>]

Returns the longest possible subsequences of the collection, in order, that don’t contain elements satisfying the given predicate.

func split(separator: Base.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Slice<Base>]

Returns the longest possible subsequences of the collection, in order, around elements equal to the given element.

func split(separator: Base.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [ArraySlice<Base.Element>]

Returns the longest possible subsequences of the sequence, in order, around elements equal to the given element.

func starts<PossiblePrefix>(with: PossiblePrefix) -> Bool

Returns a Boolean value indicating whether the initial elements of the sequence are the same as the elements in another sequence.

func starts<PossiblePrefix>(with: PossiblePrefix, by: (Base.Element, PossiblePrefix.Element) -> Bool) -> Bool

Returns a Boolean value indicating whether the initial elements of the sequence are equivalent to the elements in another sequence, using the given predicate as the equivalence test.

func suffix(Int) -> Slice<Base>

Returns a subsequence, up to the given maximum length, containing the final elements of the collection.

func suffix(from: Base.Index) -> Slice<Base>

Returns a subsequence from the specified position to the end of the collection.

func swapAt(Base.Index, Base.Index)

Exchanges the values at the specified indices of the collection.

func withContiguousMutableStorageIfAvailable<R>((inout UnsafeMutableBufferPointer<Base.Element>) -> R) -> R?

Call body(p), where p is a pointer to the collection’s mutable contiguous storage. If no such storage exists, it is first created. If the collection does not support an internal representation in a form of mutable contiguous storage, body is not called and nil is returned.

func withContiguousStorageIfAvailable<R>((UnsafeBufferPointer<Base.Element>) -> R) -> R?

Call body(p), where p is a pointer to the collection’s contiguous storage. If no such storage exists, it is first created. If the collection does not support an internal representation in a form of contiguous storage, body is not called and nil is returned.

Subscripts

subscript(Slice<Base>.Index) -> Base.Element

Accesses the element at the specified position.

subscript(Slice<Base>.Index) -> Base.Element

Accesses the element at the specified position.

subscript(Range<Base.Index>) -> Slice<Slice<Base>>

Accesses a contiguous subrange of the collection’s elements.

subscript<R>(R) -> Slice<Base>

Accesses the contiguous subrange of the collection’s elements specified by a range expression.

subscript(Range<Slice<Base>.Index>) -> Slice<Base>

Accesses a contiguous subrange of the collection’s elements.

subscript(Range<Slice<Base>.Index>) -> Slice<Base>

Accesses a contiguous subrange of the collection’s elements.

Operator Functions

static func + <Other>(Other, Slice<Base>) -> Slice<Base>

Creates a new collection by concatenating the elements of a sequence and a collection.

static func + <Other>(Slice<Base>, Other) -> Slice<Base>

Creates a new collection by concatenating the elements of a collection and a sequence.

static func + <Other>(Slice<Base>, Other) -> Slice<Base>

Creates a new collection by concatenating the elements of two collections.

static func += <Other>(inout Slice<Base>, Other)

Appends the elements of a sequence to a range-replaceable collection.

Relationships

Conforms To

Beta Software

This documentation contains preliminary information about an API or technology in development. This information is subject to change, and software implemented according to this documentation should be tested with final operating system software.

Learn more about using Apple's beta software