Structure

Substring

A slice of a string.

Overview

When you create a slice of a string, a Substring instance is the result. Operating on substrings is fast and efficient because a substring shares its storage with the original string. The Substring type presents the same interface as String, so you can avoid or defer any copying of the string’s contents.

The following example creates a greeting string, and then finds the substring of the first sentence:

let greeting = "Hi there! It's nice to meet you! 👋"
let endOfSentence = greeting.index(of: "!")!
let firstSentence = greeting[...endOfSentence]
// firstSentence == "Hi there!"

You can perform many string operations on a substring. Here, we find the length of the first sentence and create an uppercase version.

print("'\(firstSentence)' is \(firstSentence.count) characters long.")
// Prints "'Hi there!' is 9 characters long."

let shoutingSentence = firstSentence.uppercased()
// shoutingSentence == "HI THERE!"

Converting a Substring to a String

This example defines a rawData string with some unstructured data, and then uses the string’s prefix(while:) method to create a substring of the numeric prefix:

let rawInput = "126 a.b 22219 zzzzzz"
let numericPrefix = rawInput.prefix(while: { "0"..."9" ~= $0 })
// numericPrefix is the substring "126"

When you need to store a substring or pass it to a function that requires a String instance, convert it using the String.init(_:) initializer.

_ = Int(numericPrefix, radix: 10)
// error: cannot convert value...
let prefix = Int(String(numericPrefix), radix: 10)
// prefix == 126

Calling this initializer copies the contents of the substring to a new string.

Topics

Initializers

init()

Creates an empty substring.

init<S>(S)

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

init(Substring.UnicodeScalarView)

Creates a Substring having the given content.

init(Substring.UTF8View)

Creates a Substring having the given content.

init(Substring.CharacterView)

Creates a Substring having the given content.

init(Substring.UTF16View)

Creates a Substring having the given content.

init(cString: UnsafePointer<CChar>)

Creates a string from the null-terminated, UTF-8 encoded sequence of bytes at the given pointer.

init<C, Encoding>(decoding: C, as: Encoding.Type)

Creates a string from the given Unicode code units in the specified encoding.

init<Encoding>(decodingCString: UnsafePointer<Encoding.CodeUnit>, as: Encoding.Type)

Creates a string from the null-terminated sequence of bytes at the given pointer.

init(repeating: Character, count: Int)

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

Instance Properties

var count: String.IndexDistance

The number of elements in the collection.

var first: Character?

The first element of the collection.

var indices: DefaultBidirectionalIndices<Substring>

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: Character?

The last element of the collection.

var lazy: LazyCollection<Substring>

A view onto this collection that provides lazy implementations of normally eager operations, such as map and filter.

var lazy: LazySequence<Substring>

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

var lazy: LazyBidirectionalCollection<Substring>

A view onto this collection that provides lazy implementations of normally eager operations, such as map and filter.

var underestimatedCount: Int

Returns a value less than or equal to the number of elements in the sequence, nondestructively.

var underestimatedCount: Int

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

Instance Methods

func append(Character)

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 contains(Character)

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

func contains(where: (Character) -> Bool)

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

func drop(while: (Character) -> Bool)

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

func dropFirst()

Returns a subsequence containing all but the first element of the sequence.

func dropFirst(Int)

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

func dropLast()

Returns a subsequence containing all but the last element of the sequence.

func dropLast(Int)

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

func elementsEqual<OtherSequence>(OtherSequence)

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

func elementsEqual<OtherSequence>(OtherSequence, by: (Character, Character) -> 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()

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 first(where: (Character) -> Bool)

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

func forEach((Character) -> Void)

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

func index(of: Character)

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

func index(where: (Character) -> Bool)

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

func insert(Character, at: String.Index)

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

func insert<C>(contentsOf: C, at: String.Index)

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

func lexicographicallyPrecedes<OtherSequence>(OtherSequence)

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: (Character, Character) -> 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()

Returns an iterator over the elements of the collection.

func map<T>((Character) -> T)

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

func map<T>((Character) -> T)

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

func max()

Returns the maximum element in the sequence.

func max(by: (Character, Character) -> Bool)

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

func min()

Returns the minimum element in the sequence.

func min(by: (Character, Character) -> Bool)

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

func popFirst()

Removes and returns the first element of the collection.

func popLast()

Removes and returns the last element of the collection.

func prefix(Int)

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

func prefix(through: String.Index)

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

func prefix(upTo: String.Index)

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

func prefix(while: (Character) -> Bool)

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

func reduce<Result>(Result, (Result, Character) -> Result)

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

func reduce<Result>(into: Result, (inout Result, Character) -> ())

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

func remove(at: String.Index)

Removes and returns the element at the specified position.

func removeAll(keepingCapacity: Bool)

Removes all elements from the collection.

func removeFirst()

Removes and returns the first element of the collection.

func removeFirst()

Removes and returns the first element of the collection.

func removeFirst()

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 removeFirst(Int)

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

func removeFirst(Int)

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

func removeLast()

Removes and returns the last element of the collection.

func removeLast()

Removes and returns the last element of the collection.

func removeLast()

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 removeLast(Int)

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

func removeLast(Int)

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

func removeSubrange(Range<String.Index>)

Removes the elements in the specified subrange from the collection.

func removeSubrange<R>(R)

Removes the elements in the specified subrange from the collection.

func replaceSubrange<C, R>(R, with: C)

Replaces the specified subrange of elements with the given collection.

func reserveCapacity(String.IndexDistance)

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

func reversed()

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

func sorted()

Returns the elements of the sequence, sorted.

func sorted(by: (Character, Character) -> Bool)

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

func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (Character) -> Bool)

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

func split(separator: Character, maxSplits: Int, omittingEmptySubsequences: Bool)

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

func starts<PossiblePrefix>(with: PossiblePrefix)

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: (Character, Character) -> 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)

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

func suffix(from: String.Index)

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

func withCString<Result>((UnsafePointer<CChar>) -> Result)

Calls the given closure with a pointer to the contents of the string, represented as a null-terminated sequence of UTF-8 code units.

func withCString<Result, TargetEncoding>(encodedAs: TargetEncoding.Type, (UnsafePointer<TargetEncoding.CodeUnit>) -> Result)

Calls the given closure with a pointer to the contents of the string, represented as a null-terminated sequence of code units.

Operator Functions

static func !=(Substring, Substring)

Returns a Boolean value indicating whether two values are not equal.

static func ...(Substring)

Returns a partial range extending upward from a lower bound.

static func ...(Substring)

Returns a partial range up to, and including, its upper bound.

static func ..<(Substring)

Returns a partial range up to, but not including, its upper bound.

static func <=(Substring, Substring)

Returns a Boolean value indicating whether the value of the first argument is less than or equal to that of the second argument.

static func >(Substring, Substring)

Returns a Boolean value indicating whether the value of the first argument is greater than that of the second argument.

static func >=(Substring, Substring)

Returns a Boolean value indicating whether the value of the first argument is greater than or equal to that of the second argument.

See Also

Related String Types

protocol StringProtocol

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

Beta
struct String.Index

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

Beta
struct String.CharacterView

A view of a string’s contents as a collection of characters.

struct String.UnicodeScalarView

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

struct String.UTF16View

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

struct String.UTF8View

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

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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