Substring
A slice of a string.
@frozen struct SubstringWhen 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! đź‘‹"
let endOfSentence = greeting.firstIndex(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, you can convert it to a String by using the String(_:) initializer. Calling this initializer copies the contents of the substring to a new string.
func parseAndAddOne(_ s: String) -> Int {
return Int(s, radix: 10)! + 1
}
_ = parseAndAddOne(numericPrefix)
// error: cannot convert value...
let incrementedPrefix = parseAndAddOne(String(numericPrefix))
// incrementedPrefix == 127Alternatively, you can convert the function that takes a String to one that is generic over the StringProtocol protocol. The following code declares a generic version of the parseAndAddOne(_:) function:
func genericParseAndAddOne<S: StringProtocol>(_ s: S) -> Int {
return Int(s, radix: 10)! + 1
}
let genericallyIncremented = genericParseAndAddOne(numericPrefix)
// genericallyIncremented == 127You can call this generic function with an instance of either String or Substring.
Citizens in Swift
Conformances
protocol BidirectionalCollectionA collection that supports backward as well as forward traversal.
protocol CollectionA sequence whose elements can be traversed multiple times, nondestructively, and accessed by an indexed subscript.
protocol ComparableA type that can be compared using the relational operators
<,<=,>=, and>.protocol CustomDebugStringConvertibleA type with a customized textual representation suitable for debugging purposes.
protocol CustomReflectableA type that explicitly supplies its own mirror.
protocol CustomStringConvertibleA type with a customized textual representation.
protocol EquatableA type that can be compared for value equality.
protocol ExpressibleByExtendedGraphemeClusterLiteralA type that can be initialized with a string literal containing a single extended grapheme cluster.
protocol ExpressibleByStringInterpolationA type that can be initialized by string interpolation with a string literal that includes expressions.
protocol ExpressibleByStringLiteralA type that can be initialized with a string literal.
protocol ExpressibleByUnicodeScalarLiteralA type that can be initialized with a string literal containing a single Unicode scalar value.
protocol HashableA type that can be hashed into a
Hasherto produce an integer hash value.protocol LosslessStringConvertibleA type that can be represented as a string in a lossless, unambiguous way.
protocol RangeReplaceableCollectionA collection that supports replacement of an arbitrary subrange of elements with the elements of another collection.
protocol SendableA type whose values can safely be passed across concurrency domains by copying.
protocol SequenceA type that provides sequential, iterated access to its elements.
protocol StringProtocolA type that can represent a string as a collection of characters.
protocol TextOutputStreamA type that can be the target of text-streaming operations.
protocol TextOutputStreamableA source of text-streaming operations.
Members
init() Creates an empty substring.
init(Substring.UnicodeScalarView) Creates a Substring having the given content.
init(Substring.UTF8View) Creates a Substring having the given content.
init(Substring.UTF16View) Creates a Substring having the given content.
init(String) init<S>(S) 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(extendedGraphemeClusterLiteral: String) init(stringInterpolation: DefaultStringInterpolation) Creates a new instance from an interpolated string literal.
init(stringLiteral: String) init(unicodeScalarLiteral: String) var base: StringReturns the underlying string from which this substring was derived.
var customMirror: Mirrorvar debugDescription: Stringvar description: Stringvar endIndex: Substring.Indexvar isContiguousUTF8: BoolReturns whether this string is capable of providing access to validly-encoded UTF-8 contents in contiguous memory in O(1) time.
var startIndex: Substring.Indexvar unicodeScalars: Substring.UnicodeScalarViewvar utf16: Substring.UTF16Viewvar utf8: Substring.UTF8Viewsubscript(Substring.Index) -> Character subscript(Range<Substring.Index>) -> Substring static func ~= (Substring, String) -> Bool func append<S>(contentsOf: S) func distance(from: Substring.Index, to: Substring.Index) -> Int func filter((Substring.Element) throws -> Bool) rethrows -> String func index(Substring.Index, offsetBy: Int) -> Substring.Index func index(Substring.Index, offsetBy: Int, limitedBy: Substring.Index) -> Substring.Index? func index(after: Substring.Index) -> Substring.Index func index(before: Substring.Index) -> Substring.Index func lowercased() -> String func makeContiguousUTF8() If this string is not contiguous, make it so. If this mutates the substring, it will invalidate any pre-existing indices.
func replaceSubrange(Range<Substring.Index>, with: Substring) func replaceSubrange<C>(Range<Substring.Index>, with: C) func uppercased() -> String func withCString<Result>((UnsafePointer<CChar>) throws -> Result) rethrows -> 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>) throws -> Result) rethrows -> Result Calls the given closure with a pointer to the contents of the string, represented as a null-terminated sequence of code units.
func withUTF8<R>((UnsafeBufferPointer<UInt8>) throws -> R) rethrows -> R Runs
bodyover the content of this substring in contiguous memory. If this substring is not contiguous, this will first make it contiguous, which will also speed up subsequent access. If this mutates the substring, it will invalidate any pre-existing indices.func write(String) func write<Target>(to: inout Target) struct UTF16Viewstruct UTF8Viewstruct UnicodeScalarViewtypealias Indextypealias SubSequencevar characters: SubstringA view of the string’s contents as a collection of characters.
var customPlaygroundQuickLook: _PlaygroundQuickLookfunc withMutableCharacters<R>((inout Substring) -> R) -> R Applies the given closure to a mutable view of the string’s characters.
typealias CharacterViewA view of a string’s contents as a collection of characters.
Features
var first: Self.Element?The first element of the collection.
var last: Self.Element?The last element of the collection.
var lazy: LazySequence<Self>A sequence containing the same elements as this sequence, but on which some operations, such as
mapandfilter, are implemented lazily.static func != (Self, Self) -> Bool static func != <RHS>(Self, RHS) -> Bool static func + <Other>(Other, Self) -> Self Creates a new collection by concatenating the elements of a sequence and a collection.
static func + <Other>(Self, Other) -> Self Creates a new collection by concatenating the elements of a collection and a sequence.
static func + <Other>(Self, Other) -> Self Creates a new collection by concatenating the elements of two collections.
static func += <Other>(inout Self, Other) Appends the elements of a sequence to a range-replaceable collection.
static func ... (Self) -> PartialRangeFrom<Self> Returns a partial range extending upward from a lower bound.
static func ... (Self) -> PartialRangeThrough<Self> Returns a partial range up to, and including, its upper bound.
static func ... (Self, Self) -> ClosedRange<Self> Returns a closed range that contains both of its bounds.
static func ..< (Self) -> PartialRangeUpTo<Self> Returns a partial range up to, but not including, its upper bound.
static func ..< (Self, Self) -> Range<Self> Returns a half-open range that contains its lower bound but not its upper bound.
static func == <RHS>(Self, RHS) -> Bool func allSatisfy((Self.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether every element of a sequence satisfies a given predicate.
func applying(CollectionDifference<Self.Element>) -> Self? Applies the given difference to this collection.
func compactMap<ElementOfResult>((Self.Element) throws -> ElementOfResult?) rethrows -> [ElementOfResult] Returns an array containing the non-
nilresults of calling the given transformation with each element of this sequence.func contains(Self.Element) -> Bool Returns a Boolean value indicating whether the sequence contains the given element.
func contains(where: (Self.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.
func difference<C>(from: C) -> CollectionDifference<Self.Element> Returns the difference needed to produce this collection’s ordered elements from the given collection.
func difference<C>(from: C, by: (C.Element, Self.Element) -> Bool) -> CollectionDifference<Self.Element> 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: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence Returns a subsequence by skipping elements while
predicatereturnstrueand returning the remaining elements.func dropFirst(Int) -> Self.SubSequence Returns a subsequence containing all but the given number of initial elements.
func dropLast(Int) -> Self.SubSequence 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: (Self.Element, OtherSequence.Element) throws -> Bool) rethrows -> 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<Self> 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: (Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the first element of the sequence that satisfies the given predicate.
func firstIndex(of: Self.Element) -> Self.Index? Returns the first index where the specified value appears in the collection.
func firstIndex(where: (Self.Element) throws -> Bool) rethrows -> Self.Index? Returns the first index in which an element of the collection satisfies the given predicate.
func flatMap<SegmentOfResult>((Self.Element) throws -> SegmentOfResult) rethrows -> [SegmentOfResult.Element] Returns an array containing the concatenated results of calling the given transformation with each element of this sequence.
func forEach((Self.Element) throws -> Void) rethrows Calls the given closure on each element in the sequence in the same order as a
for-inloop.func formIndex(inout Self.Index, offsetBy: Int) Offsets the given index by the specified distance.
func formIndex(inout Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Bool Offsets the given index by the specified distance, or so that it equals the given limiting index.
func last(where: (Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the last element of the sequence that satisfies the given predicate.
func lastIndex(of: Self.Element) -> Self.Index? Returns the last index where the specified value appears in the collection.
func lastIndex(where: (Self.Element) throws -> Bool) rethrows -> Self.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: (Self.Element, Self.Element) throws -> Bool) rethrows -> 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 map<T>((Self.Element) throws -> T) rethrows -> [T] Returns an array containing the results of mapping the given closure over the sequence’s elements.
func map<T>((Self.Element) throws -> T) rethrows -> [T] Returns an array containing the results of mapping the given closure over the sequence’s elements.
func max() -> Self.Element? Returns the maximum element in the sequence.
func max(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the maximum element in the sequence, using the given predicate as the comparison between elements.
func min() -> Self.Element? Returns the minimum element in the sequence.
func min(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the minimum element in the sequence, using the given predicate as the comparison between elements.
func popFirst() -> Self.Element? Removes and returns the first element of the collection.
func popLast() -> Self.Element? Removes and returns the last element of the collection.
func popLast() -> Self.Element? Removes and returns the last element of the collection.
func popLast() -> Self.Element? Removes and returns the last element of the collection.
func prefix(Int) -> Self.SubSequence Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.
func prefix(through: Self.Index) -> Self.SubSequence Returns a subsequence from the start of the collection through the specified position.
func prefix(upTo: Self.Index) -> Self.SubSequence Returns a subsequence from the start of the collection up to, but not including, the specified position.
func prefix(while: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence Returns a subsequence containing the initial elements until
predicatereturnsfalseand skipping the remaining elements.func randomElement() -> Self.Element? Returns a random element of the collection.
func randomElement<T>(using: inout T) -> Self.Element? Returns a random element of the collection, using the given generator as a source for randomness.
func reduce<Result>(Result, (Result, Self.Element) throws -> Result) rethrows -> Result Returns the result of combining the elements of the sequence using the given closure.
func reduce<Result>(into: Result, (inout Result, Self.Element) throws -> ()) rethrows -> Result Returns the result of combining the elements of the sequence using the given closure.
func removeFirst() -> Self.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() -> Self.Element Removes and returns the last element of the collection.
func removeLast() -> Self.Element Removes and returns the last element of the collection.
func removeLast() -> Self.Element Removes and returns the last element 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 removeLast(Int) Removes the specified number of elements from the end of the collection.
func reversed() -> ReversedCollection<Self> Returns a view presenting the elements of the collection in reverse order.
func shuffled() -> [Self.Element] Returns the elements of the sequence, shuffled.
func shuffled<T>(using: inout T) -> [Self.Element] Returns the elements of the sequence, shuffled using the given generator as a source for randomness.
func sorted() -> [Self.Element] Returns the elements of the sequence, sorted.
func sorted(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> [Self.Element] Returns the elements of the sequence, sorted using the given predicate as the comparison between elements.
func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (Self.Element) throws -> Bool) rethrows -> [Self.SubSequence] Returns the longest possible subsequences of the collection, in order, that don’t contain elements satisfying the given predicate.
func split(separator: Self.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Self.SubSequence] 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: (Self.Element, PossiblePrefix.Element) throws -> Bool) rethrows -> 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) -> Self.SubSequence Returns a subsequence, up to the given maximum length, containing the final elements of the collection.
func suffix(from: Self.Index) -> Self.SubSequence Returns a subsequence from the specified position to the end of the collection.
func flatMap<ElementOfResult>((Self.Element) throws -> ElementOfResult?) rethrows -> [ElementOfResult] func index(of: Self.Element) -> Self.Index? Returns the first index where the specified value appears in the collection.
Available in RegexBuilder
Conformances
protocol RegexComponentA type that represents a regular expression.
Members
Extension in JSONEncoding
Conformances
protocol JSONEncodableA type that can be encoded to a JSON variant value.
Members
func encoded(as: JSON.Type) -> JSON Encodes this substring as a value of
JSON.string(_:).
Extension in BSONEncoding
Conformances
protocol BSONEncodableA type that can be encoded to a BSON variant value.
Members
func encode(to: inout BSON.Field) Encodes this substring as a value of type
BSON.string.
Extension in SwiftSyntaxBuilder
Conformances
protocol ExpressibleByLiteralSyntaxA Swift type whose value can be represented directly in source code by a Swift literal.