Structure

String.UTF16View

A view of a string’s contents as a collection of UTF-16 code units.

Declaration

@frozen struct UTF16View

Overview

You can access a string’s view of UTF-16 code units by using its utf16 property. A string’s UTF-16 view encodes the string’s Unicode scalar values as 16-bit integers.

let flowers = "Flowers 💐"
for v in flowers.utf16 {
    print(v)
}
// 70
// 108
// 111
// 119
// 101
// 114
// 115
// 32
// 55357
// 56464

Unicode scalar values that make up a string’s contents can be up to 21 bits long. The longer scalar values may need two UInt16 values for storage. Those “pairs” of code units are called surrogate pairs.

let flowermoji = "💐"
for v in flowermoji.unicodeScalars {
    print(v, v.value)
}
// 💐 128144

for v in flowermoji.utf16 {
    print(v)
}
// 55357
// 56464

To convert a String.UTF16View instance back into a string, use the String type’s init(_:) initializer.

let favemoji = "My favorite emoji is 🎉"
if let i = favemoji.utf16.firstIndex(where: { $0 >= 128 }) {
    let asciiPrefix = String(favemoji.utf16[..<i])
    print(asciiPrefix)
}
// Prints "My favorite emoji is "

UTF16View Elements Match NSString Characters

The UTF-16 code units of a string’s utf16 view match the elements accessed through indexed NSString APIs.

print(flowers.utf16.count)
// Prints "10"

let nsflowers = flowers as NSString
print(nsflowers.length)
// Prints "10"

Unlike NSString, however, String.UTF16View does not use integer indices. If you need to access a specific position in a UTF-16 view, use Swift’s index manipulation methods. The following example accesses the fourth code unit in both the flowers and nsflowers strings:

print(nsflowers.character(at: 3))
// Prints "119"

let i = flowers.utf16.index(flowers.utf16.startIndex, offsetBy: 3)
print(flowers.utf16[i])
// Prints "119"

Although the Swift overlay updates many Objective-C methods to return native Swift indices and index ranges, some still return instances of NSRange. To convert an NSRange instance to a range of String.Index, use the Range(_:in:) initializer, which takes an NSRange and a string as arguments.

let snowy = "❄️ Let it snow! ☃️"
let nsrange = NSRange(location: 3, length: 12)
if let range = Range(nsrange, in: snowy) {
    print(snowy[range])
}
// Prints "Let it snow!"

Topics

Type Aliases

typealias String.UTF16View.Index

A type that represents a position in the collection.

typealias String.UTF16View.Element

A type representing the sequence’s elements.

Beta
typealias String.UTF16View.Indices

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

Beta
typealias String.UTF16View.SubSequence

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

Instance Properties

var count: Int

The number of elements in the collection.

var customMirror: Mirror

Returns a mirror that reflects the UTF-16 view of a string.

var customPlaygroundQuickLook: _PlaygroundQuickLook

A custom playground Quick Look for this instance.

Deprecated
var debugDescription: String

A textual representation of this instance, suitable for debugging.

var description: String

A textual representation of this instance.

var endIndex: String.UTF16View.Index

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

var first: UTF16.CodeUnit?

The first element of the collection.

var indices: DefaultIndices<String.UTF16View>

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: UTF16.CodeUnit?

The last element of the collection.

var lazy: LazySequence<String.UTF16View>

A sequence containing the same elements as this sequence, but on which some operations, such as map and filter, are implemented lazily.

var startIndex: String.UTF16View.Index

The position of the first code unit if the String is nonempty; identical to endIndex otherwise.

var underestimatedCount: Int

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

Instance Methods

func allSatisfy((UTF16.CodeUnit) -> Bool) -> Bool

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

func compactMap<ElementOfResult>((UTF16.CodeUnit) -> ElementOfResult?) -> [ElementOfResult]

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

func contains(UTF16.CodeUnit) -> Bool

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

func contains(where: (UTF16.CodeUnit) -> Bool) -> Bool

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

func difference<C>(from: C) -> CollectionDifference<UTF16.CodeUnit>

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

Beta
func difference<C>(from: C, by: (C.Element, UTF16.CodeUnit) -> Bool) -> CollectionDifference<UTF16.CodeUnit>

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: (UTF16.CodeUnit) -> Bool) -> Substring.UTF16View

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

func dropFirst(Int) -> Substring.UTF16View

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

func dropLast(Int) -> Substring.UTF16View

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: (UTF16.CodeUnit, 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<String.UTF16View>

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((UTF16.CodeUnit) -> Bool) -> [UTF16.CodeUnit]

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

func first(where: (UTF16.CodeUnit) -> Bool) -> UTF16.CodeUnit?

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

func firstIndex(of: UTF16.CodeUnit) -> String.Index?

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

func firstIndex(where: (UTF16.CodeUnit) -> Bool) -> String.Index?

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

func flatMap<SegmentOfResult>((UTF16.CodeUnit) -> SegmentOfResult) -> [SegmentOfResult.Element]

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

func forEach((UTF16.CodeUnit) -> Void)

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

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

Offsets the given index by the specified distance.

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

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

func formIndex(after: inout String.Index)

Replaces the given index with its successor.

func formIndex(before: inout String.Index)

Replaces the given index with its predecessor.

func index(String.UTF16View.Index, offsetBy: Int) -> String.UTF16View.Index

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

func index(String.UTF16View.Index, offsetBy: Int, limitedBy: String.UTF16View.Index) -> String.UTF16View.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: String.UTF16View.Index) -> String.UTF16View.Index

Returns the position immediately after the given index.

func index(before: String.UTF16View.Index) -> String.UTF16View.Index

Returns the position immediately before the given index.

func index(of: UTF16.CodeUnit) -> String.Index?

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

Deprecated
func last(where: (UTF16.CodeUnit) -> Bool) -> UTF16.CodeUnit?

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

func lastIndex(of: UTF16.CodeUnit) -> String.Index?

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

func lastIndex(where: (UTF16.CodeUnit) -> Bool) -> String.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: (UTF16.CodeUnit, UTF16.CodeUnit) -> 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() -> String.UTF16View.Iterator

Returns an iterator over the elements of the collection.

func map<T>((UTF16.CodeUnit) -> T) -> [T]

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

func max() -> UTF16.CodeUnit?

Returns the maximum element in the sequence.

func max(by: (UTF16.CodeUnit, UTF16.CodeUnit) -> Bool) -> UTF16.CodeUnit?

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

func min() -> UTF16.CodeUnit?

Returns the minimum element in the sequence.

func min(by: (UTF16.CodeUnit, UTF16.CodeUnit) -> Bool) -> UTF16.CodeUnit?

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

func prefix(Int) -> Substring.UTF16View

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

func prefix(through: String.Index) -> Substring.UTF16View

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

func prefix(upTo: String.Index) -> Substring.UTF16View

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

func prefix(while: (UTF16.CodeUnit) -> Bool) -> Substring.UTF16View

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

func randomElement() -> UTF16.CodeUnit?

Returns a random element of the collection.

func randomElement<T>(using: inout T) -> UTF16.CodeUnit?

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

func reduce<Result>(Result, (Result, UTF16.CodeUnit) -> Result) -> Result

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

func reduce<Result>(into: Result, (inout Result, UTF16.CodeUnit) -> ()) -> Result

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

func reversed() -> ReversedCollection<String.UTF16View>

Returns a view presenting the elements of the collection in reverse order.

func shuffled() -> [UTF16.CodeUnit]

Returns the elements of the sequence, shuffled.

func shuffled<T>(using: inout T) -> [UTF16.CodeUnit]

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

func sorted() -> [UTF16.CodeUnit]

Returns the elements of the sequence, sorted.

func sorted(by: (UTF16.CodeUnit, UTF16.CodeUnit) -> Bool) -> [UTF16.CodeUnit]

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

func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (UTF16.CodeUnit) -> Bool) -> [Substring.UTF16View]

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

func split(separator: UTF16.CodeUnit, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Substring.UTF16View]

Returns the longest possible subsequences of the collection, 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: (UTF16.CodeUnit, 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) -> Substring.UTF16View

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

func suffix(from: String.Index) -> Substring.UTF16View

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

func withContiguousStorageIfAvailable<R>((UnsafeBufferPointer<UTF16.CodeUnit>) -> 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(Range<String.UTF16View.Index>) -> Substring.UTF16View

Accesses a contiguous subrange of the collection’s elements.

subscript(String.UTF16View.Index) -> UTF16.CodeUnit

Accesses the code unit at the given position.

subscript<R>(R) -> Substring.UTF16View

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

Structures

struct String.UTF16View.Iterator

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

Relationships

From Protocol

See Also

Related String Types

struct Substring

A slice of a string.

protocol StringProtocol

A type that can represent a string as a collection of characters.

struct String.Index

A position of a character or code unit in a string.

struct String.UnicodeScalarView

A view of a string’s contents as a collection of Unicode scalar values.

struct String.UTF8View

A view of a string’s contents as a collection of UTF-8 code units.

struct String.Iterator

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

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.

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