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.

typealias String.UTF16View.Indices

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

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.

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.

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.