structString
| Inheritance |
Comparable, CustomDebugStringConvertible, Equatable, ExtendedGraphemeClusterLiteralConvertible, Hashable, MirrorPathType, OutputStreamType, Streamable, StringInterpolationConvertible, StringLiteralConvertible, UnicodeScalarLiteralConvertible, _ObjectiveCBridgeable, _Reflectable
View Protocol Hierarchy →
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|---|---|
| Associated Types |
The index type for subscripting a
The index type for subscripting a
The index type for subscripting a |
| Nested Types | String.CharacterView, String.UnicodeScalarView, String.UTF16View, String.UTF8View, String.CharacterView.Index, String.UnicodeScalarView.Index, String.UnicodeScalarView.Generator, String.UTF16View.Index, String.UTF8View.Index |
| Import |
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Initializers
An empty String.
Declaration
init()
[Foundation]
Declaration
init(_cocoaString:NSString)
Construct the String corresponding to the given sequence of
Unicode scalars.
Declaration
init(_characters:String.CharacterView)
Construct the String corresponding to the given sequence of
Unicode scalars.
Declaration
init(_unicodeScalars:String.UnicodeScalarView)
Initialize self with the textual representation of instance.
- If
Tconforms toStreamable, the result is obtained by callinginstance.writeTo(s)on an empty string s. - Otherwise, if
Tconforms toCustomStringConvertible, the result isinstance'sdescription - Otherwise, if
Tconforms toCustomDebugStringConvertible, the result isinstance'sdebugDescription - Otherwise, an unspecified result is supplied automatically by the Swift standard library.
See Also: String.init<T>(reflecting: T)
Declaration
init<T>(_instance:T)
Create an instance containing characters.
Declaration
init<S:SequenceTypewhereS.Generator.Element==Character>(_characters:S)
Create an instance representing v in the given radix (base).
Numerals greater than 9 are represented as roman letters,
starting with a if uppercase is false or A otherwise.
Declaration
init<T:_SignedIntegerType>(_v:T,radix:Int,uppercase:Bool=default)
Create an instance representing v in the given radix (base).
Numerals greater than 9 are represented as roman letters,
starting with a if uppercase is false or A otherwise.
Declaration
init<T:UnsignedIntegerType>(_v:T,radix:Int,uppercase:Bool=default)
Declaration
init(_builtinExtendedGraphemeClusterLiteralstart:Builtin.RawPointer,byteSize:Builtin.Word,isASCII:Builtin.Int1)
Declaration
init(_builtinStringLiteralstart:Builtin.RawPointer,byteSize:Builtin.Word,isASCII:Builtin.Int1)
Declaration
init(_builtinUTF16StringLiteralstart:Builtin.RawPointer,numberOfCodeUnits:Builtin.Word)
Declaration
init(_builtinUnicodeScalarLiteralvalue:Builtin.Int32)
[Foundation] Produces a string created by reading data from the file at a given path interpreted using a given encoding.
Declaration
init(contentsOfFilepath:String,encodingenc:NSStringEncoding)
[Foundation] Produces a string created by reading data from the file at a given path and returns by reference the encoding used to interpret the file.
Declaration
init(contentsOfFilepath:String,usedEncoding:UnsafeMutablePointer<NSStringEncoding>=default)
[Foundation] Produces a string created by reading data from a given URL
interpreted using a given encoding. Errors are written into the
inout error argument.
Declaration
init(contentsOfURLurl:NSURL,encodingenc:NSStringEncoding)
[Foundation] Produces a string created by reading data from a given URL
and returns by reference the encoding used to interpret the
data. Errors are written into the inout error argument.
Declaration
init(contentsOfURLurl:NSURL,usedEncodingenc:UnsafeMutablePointer<NSStringEncoding>=default)
Construct an instance that is the concatenation of count copies
of Character(repeatedValue).
Declaration
init(count:Int,repeatedValuec:UnicodeScalar)
Create an instance initialized to value.
Declaration
init(extendedGraphemeClusterLiteralvalue:String)
[Foundation] Returns a String object initialized by using a given
format string as a template into which the remaining argument
values are substituted.
Declaration
init(format:String,_arguments:CVarArgType...)
[Foundation] Returns a String object initialized by using a given
format string as a template into which the remaining argument
values are substituted according to the user’s default locale.
Declaration
init(format:String,arguments: [CVarArgType])
[Foundation] Returns a String object initialized by using a given
format string as a template into which the remaining argument
values are substituted according to given locale information.
Declaration
init(format:String,locale:NSLocale?,_args:CVarArgType...)
[Foundation] Returns a String object initialized by using a given
format string as a template into which the remaining argument
values are substituted according to given locale information.
Declaration
init(format:String,locale:NSLocale?,arguments: [CVarArgType])
Initialize self with a detailed textual representation of
subject, suitable for debugging.
-
If
Tconforms toCustomDebugStringConvertible, the result issubject'sdebugDescription. -
Otherwise, if
Tconforms toCustomStringConvertible, the result issubject'sdescription. -
Otherwise, if
Tconforms toStreamable, the result is obtained by callingsubject.writeTo(s)on an empty string s. -
Otherwise, an unspecified result is supplied automatically by the Swift standard library.
See Also: String.init<T>(T)
Declaration
init<T>(reflectingsubject:T)
Create an instance by concatenating the elements of strings.
Declaration
init(stringInterpolationstrings:String...)
Declaration
init(stringInterpolationSegmentexpr:Bool)
Declaration
init(stringInterpolationSegmentexpr:Character)
Declaration
init(stringInterpolationSegmentexpr:Float32)
Declaration
init(stringInterpolationSegmentexpr:Float64)
Declaration
init(stringInterpolationSegmentexpr:Int)
Declaration
init(stringInterpolationSegmentexpr:Int8)
Declaration
init(stringInterpolationSegmentexpr:Int16)
Declaration
init(stringInterpolationSegmentexpr:Int32)
Declaration
init(stringInterpolationSegmentexpr:Int64)
Declaration
init(stringInterpolationSegmentexpr:String)
Declaration
init(stringInterpolationSegmentexpr:UInt)
Declaration
init(stringInterpolationSegmentexpr:UInt8)
Declaration
init(stringInterpolationSegmentexpr:UInt16)
Declaration
init(stringInterpolationSegmentexpr:UInt32)
Declaration
init(stringInterpolationSegmentexpr:UInt64)
Declaration
init(stringInterpolationSegmentexpr:UnicodeScalar)
Create an instance containing expr's print representation.
Declaration
init<T>(stringInterpolationSegmentexpr:T)
[Foundation] Returns an initialized String object that contains a
given number of characters from a given array of Unicode
characters.
Declaration
init(utf16CodeUnits:UnsafePointer<unichar>,count:Int)
[Foundation] Returns an initialized String object that contains a given
number of characters from a given array of UTF-16 Code Units
Declaration
init(utf16CodeUnitsNoCopy:UnsafePointer<unichar>,count:Int,freeWhenDoneflag:Bool)
Construct the String corresponding to the given sequence of
UTF-8 code units. If utf8 contains unpaired surrogates, the
result is nil.
Declaration
init?(_utf8:String.UTF8View)
Construct the String corresponding to the given sequence of
UTF-16 code units. If utf16 contains unpaired surrogates, the
result is nil.
Declaration
init?(_utf16:String.UTF16View)
[Foundation] Produces a string containing the bytes in a given C array, interpreted according to a given encoding.
Declaration
init?(CString:UnsafePointer<CChar>,encodingenc:NSStringEncoding)
[Foundation] Produces a string created by copying the data from a given C array of UTF8-encoded bytes.
Declaration
init?(UTF8Stringbytes:UnsafePointer<CChar>)
[Foundation] Produces an initialized NSString object equivalent to the given
bytes interpreted in the given encoding.
Declaration
init?<S:SequenceTypewhereS.Generator.Element==UInt8>(bytes:S,encoding:NSStringEncoding)
[Foundation] Produces an initialized String object that contains a
given number of bytes from a given buffer of bytes interpreted
in a given encoding, and optionally frees the buffer. WARNING:
this initializer is not memory-safe!
Declaration
init?(bytesNoCopybytes:UnsafeMutablePointer<Void>,length:Int,encoding:NSStringEncoding,freeWhenDoneflag:Bool)
[Foundation] Returns a String initialized by converting given data into
Unicode characters using a given encoding.
Declaration
init?(data:NSData,encoding:NSStringEncoding)
Instance Variables
[Foundation] Produce a string with the first character from each word changed to the corresponding uppercase value.
Declaration
varcapitalizedString:String{get}
A collection of Characters representing the String's
extended grapheme
clusters.
Declaration
varcharacters:String.CharacterView{get}
A textual representation of self, suitable for debugging.
Declaration
vardebugDescription:String{get}
[Foundation] Returns a string made by normalizing the String’s
contents using Form D.
Declaration
vardecomposedStringWithCanonicalMapping:String{get}
[Foundation] Returns a string made by normalizing the String’s
contents using Form KD.
Declaration
vardecomposedStringWithCompatibilityMapping:String{get}
The "past the end" position in self.characters.
endIndex is not a valid argument to subscript, and is always
reachable from startIndex by zero or more applications of
successor().
Declaration
varendIndex:Index{get}
[Foundation] Returns the fastest encoding to which the String may be
converted without loss of information.
Declaration
varfastestEncoding:NSStringEncoding{get}
[Foundation] An unsigned integer that can be used as a hash table address.
Declaration
varhash:Int{get}
The hash value.
Axiom: x == y implies x.hashValue == y.hashValue.
Note: The hash value is not guaranteed to be stable across different invocations of the same program. Do not persist the hash value across program runs.
Declaration
varhashValue:Int{get}
[Foundation] A capitalized representation of the String that is produced
using the current locale.
Declaration
varlocalizedCapitalizedString:String{get}
[Foundation] A lowercase version of the string that is produced using the current locale.
Declaration
varlocalizedLowercaseString:String{get}
[Foundation] An uppercase version of the string that is produced using the current locale.
Declaration
varlocalizedUppercaseString:String{get}
Declaration
varlowercaseString:String{get}
A contiguously-stored nul-terminated UTF-8 representation of
self.
To access the underlying memory, invoke
withUnsafeBufferPointer on the ContiguousArray.
Declaration
varnulTerminatedUTF8:ContiguousArray<CodeUnit>{get}
[Foundation] Returns a string made by normalizing the String’s
contents using Form C.
Declaration
varprecomposedStringWithCanonicalMapping:String{get}
[Foundation] Returns a string made by normalizing the String’s
contents using Form KC.
Declaration
varprecomposedStringWithCompatibilityMapping:String{get}
[Foundation] Returns the smallest encoding to which the String can
be converted without loss of information.
Declaration
varsmallestEncoding:NSStringEncoding{get}
The position of the first Character in self.characters if
self is non-empty; identical to endIndex otherwise.
Declaration
varstartIndex:Index{get}
[Foundation] Returns a new string made from the String by replacing
all percent encoded sequences with the matching UTF-8
characters.
Declaration
varstringByRemovingPercentEncoding:String? {get}
The value of self as a collection of Unicode scalar values.
Declaration
varunicodeScalars:String.UnicodeScalarView{getset}
Declaration
varuppercaseString:String{get}
Subscripts
Declaration
subscript(i:Index) ->Character{get}
Static Methods
[Foundation] Returns an Array of the encodings string objects support in the application’s environment.
Declaration
staticfuncavailableStringEncodings() ->[NSStringEncoding]
[Foundation] Returns the C-string encoding assumed for any method accepting a C string as an argument.
Declaration
staticfuncdefaultCStringEncoding() ->NSStringEncoding
Creates a new String by copying the nul-terminated UTF-8 data
referenced by a CString.
Returns nil if the CString is NULL or if it contains ill-formed
UTF-8 code unit sequences.
Declaration
staticfuncfromCString(cs:UnsafePointer<CChar>) ->String?
Creates a new String by copying the nul-terminated UTF-8 data
referenced by a CString.
Returns nil if the CString is NULL. If CString contains
ill-formed UTF-8 code unit sequences, replaces them with replacement
characters (U+FFFD).
Declaration
staticfuncfromCStringRepairingIllFormedUTF8(cs:UnsafePointer<CChar>) ->(String?,hadError:Bool)
Returns a human-readable string giving the name of a given encoding.
Declaration
staticfunclocalizedNameOfStringEncoding(encoding:NSStringEncoding) ->String
[Foundation] Returns a string created by using a given format string as a template into which the remaining argument values are substituted according to the user's default locale.
Declaration
staticfunclocalizedStringWithFormat(format:String,_arguments:CVarArgType...) ->String
Instance Methods
Declaration
mutatingfuncappend(c:Character)
Declaration
mutatingfuncappendContentsOf<S:SequenceTypewhereS.Generator.Element==Character>(newElements:S)
[Foundation] Returns a representation of the String as a C string
using a given encoding.
Declaration
funccStringUsingEncoding(encoding:NSStringEncoding) ->[CChar]?
[Foundation] Returns a Boolean value that indicates whether the
String can be converted to a given encoding without loss of
information.
Declaration
funccanBeConvertedToEncoding(encoding:NSStringEncoding) ->Bool
[Foundation] Returns a capitalized representation of the String
using the specified locale.
Declaration
funccapitalizedStringWithLocale(locale:NSLocale?) ->String
[Foundation] Returns the result of invoking compare:options: with
NSCaseInsensitiveSearch as the only option.
Declaration
funccaseInsensitiveCompare(aString:String) ->NSComparisonResult
[Foundation] Interprets the String as a path in the file system and
attempts to perform filename completion, returning a numeric
value that indicates whether a match was possible, and by
reference the longest path that matches the String.
Returns the actual number of matching paths.
Declaration
funccompletePathIntoString(outputName:UnsafeMutablePointer<String>=default,caseSensitive:Bool,matchesIntoArray:UnsafeMutablePointer<[String]>=default,filterTypes: [String]? =default) ->Int
[Foundation] Returns an array containing substrings from the String
that have been divided by characters in a given set.
Declaration
funccomponentsSeparatedByCharactersInSet(separator:NSCharacterSet) ->[String]
[Foundation] Returns an NSData object containing a representation of
the String encoded using a given encoding.
Declaration
funcdataUsingEncoding(encoding:NSStringEncoding,allowLossyConversion:Bool=default) ->NSData?
[Foundation] Performs linguistic analysis on the specified string by enumerating the specific range of the string, providing the Block with the located tags.
Declaration
[Foundation] Enumerates the substrings of the specified type in the specified range of the string.
Declaration
[Foundation] Writes the given range of characters into buffer in a given
encoding, without any allocations. Does not NULL-terminate.
buffer: A buffer into which to store the bytes from
the receiver. The returned bytes are not NUL-terminated.
maxBufferCount: The maximum number of bytes to write
to buffer.
usedBufferCount: The number of bytes used from
buffer. Pass nil if you do not need this value.
encoding: The encoding to use for the returned bytes.
options: A mask to specify options to use for
converting the receiver’s contents to encoding (if conversion
is necessary).
range: The range of characters in the receiver to get.
leftover: The remaining range. Pass nil If you do
not need this value.
Returns: true iff some characters were converted.
Note: Conversion stops when the buffer fills or when the conversion isn't possible due to the chosen encoding.
Note: will get a maximum of min(buffer.count, maxLength) bytes.
Declaration
funcgetBytes(inoutbuffer: [UInt8],maxLengthmaxBufferCount:Int,usedLengthusedBufferCount:UnsafeMutablePointer<Int>,encoding:NSStringEncoding,options:NSStringEncodingConversionOptions,range:Range<Index>,remainingRangeleftover:UnsafeMutablePointer<Range<Index>>) ->Bool
[Foundation] Returns by reference the beginning of the first line and the end of the last line touched by the given range.
Declaration
funcgetLineStart(start:UnsafeMutablePointer<Index>,end:UnsafeMutablePointer<Index>,contentsEnd:UnsafeMutablePointer<Index>,forRange:Range<Index>)
[Foundation] Returns by reference the beginning of the first paragraph and the end of the last paragraph touched by the given range.
Declaration
funcgetParagraphStart(start:UnsafeMutablePointer<Index>,end:UnsafeMutablePointer<Index>,contentsEnd:UnsafeMutablePointer<Index>,forRange:Range<Index>)
Insert newElement at index i.
Invalidates all indices with respect to self.
Complexity: O(self.count).
Declaration
mutatingfuncinsert(newElement:Character,atIndexi:Index)
Insert newElements at index i.
Invalidates all indices with respect to self.
Complexity: O(self.count + newElements.count).
Declaration
mutatingfuncinsertContentsOf<S:CollectionTypewhereS.Generator.Element==Character>(newElements:S,ati:Index)
[Foundation] Returns the number of bytes required to store the
String in a given encoding.
Declaration
funclengthOfBytesUsingEncoding(encoding:NSStringEncoding) ->Int
[Foundation] Returns an array of linguistic tags for the specified range and requested tags within the receiving string.
Declaration
funclinguisticTagsInRange(range:Range<Index>,schemetagScheme:String,optionsopts:NSLinguisticTaggerOptions=default,orthography:NSOrthography? =default,tokenRanges:UnsafeMutablePointer<[Range<Index>]>=default) ->[String]
[Foundation] Compares the string and a given string using a case-insensitive, localized, comparison.
Declaration
funclocalizedCaseInsensitiveCompare(aString:String) ->NSComparisonResult
[Foundation] Returns true iff other is non-empty and contained within
self by case-insensitive, non-literal search, taking into
account the current locale.
Locale-independent case-insensitive operation, and other needs,
can be achieved by calling
rangeOfString(_:options:,range:_locale:_).
Equivalent to
self.rangeOfString(other,options: .CaseInsensitiveSearch,locale:NSLocale.currentLocale()) !=nil
Declaration
[Foundation] Compares the string and a given string using a localized comparison.
Declaration
funclocalizedCompare(aString:String) ->NSComparisonResult
[Foundation] Compares strings as sorted by the Finder.
Declaration
funclocalizedStandardCompare(string:String) ->NSComparisonResult
[Foundation] Returns true if self contains string, taking the current locale
into account.
This is the most appropriate method for doing user-level string searches, similar to how searches are done generally in the system. The search is locale-aware, case and diacritic insensitive. The exact list of search options applied may change over time.
Declaration
[Foundation] Finds and returns the range of the first occurrence of a given string,
taking the current locale into account. Returns nil if the string was
not found.
This is the most appropriate method for doing user-level string searches, similar to how searches are done generally in the system. The search is locale-aware, case and diacritic insensitive. The exact list of search options applied may change over time.
Declaration
[Foundation] Returns a version of the string with all letters converted to lowercase, taking into account the specified locale.
Declaration
funclowercaseStringWithLocale(locale:NSLocale?) ->String
[Foundation] Returns the maximum number of bytes needed to store the
String in a given encoding.
Declaration
funcmaximumLengthOfBytesUsingEncoding(encoding:NSStringEncoding) ->Int
[Foundation] Parses the String as a text representation of a
property list, returning an NSString, NSData, NSArray, or
NSDictionary object, according to the topmost element.
Declaration
funcpropertyList() ->AnyObject
[Foundation] Finds and returns the range in the String of the first
character from a given character set found in a given range with
given options.
Declaration
[Foundation] Returns the range in the String of the composed
character sequence located at a given index.
Declaration
funcrangeOfComposedCharacterSequenceAtIndex(anIndex:Index) ->Range<Index>
[Foundation] Finds and returns the range of the first occurrence of a
given string within a given range of the String, subject to
given options, using the specified locale, if any.
Declaration
Remove all characters.
Invalidates all indices with respect to self.
keepCapacity: If true, prevents the release of
allocated storage, which can be a useful optimization
when self is going to be grown again.
Declaration
mutatingfuncremoveAll(keepCapacitykeepCapacity:Bool=default)
Remove and return the element at index i.
Invalidates all indices with respect to self.
Complexity: O(self.count).
Declaration
mutatingfuncremoveAtIndex(i:Index) ->Character
Remove the indicated subRange of characters.
Invalidates all indices with respect to self.
Complexity: O(self.count).
Declaration
mutatingfuncremoveRange(subRange:Range<Index>)
Replace the given subRange of elements with newElements.
Invalidates all indices with respect to self.
Complexity: O(subRange.count) if subRange.endIndex
== self.endIndex and newElements.isEmpty, O(N) otherwise.
Declaration
Replace the given subRange of elements with newElements.
Invalidates all indices with respect to self.
Complexity: O(subRange.count) if subRange.endIndex
== self.endIndex and newElements.isEmpty, O(N) otherwise.
Declaration
mutatingfuncreplaceRange<C:CollectionTypewhereC.Generator.Element==Character>(subRange:Range<Index>,withnewElements:C)
Declaration
mutatingfuncreserveCapacity(n:Int)
[Foundation] Returns a new string made from the String by replacing
all characters not in the specified set with percent encoded
characters.
Declaration
funcstringByAddingPercentEncodingWithAllowedCharacters(allowedCharacters:NSCharacterSet) ->String?
[Foundation] Returns a representation of the String using a given
encoding to determine the percent escapes necessary to convert
the String into a legal URL string.
Declaration
funcstringByAddingPercentEscapesUsingEncoding(encoding:NSStringEncoding) ->String?
[Foundation] Returns a string made by appending to the String a
string constructed from a given format string and the following
arguments.
Declaration
funcstringByAppendingFormat(format:String,_arguments:CVarArgType...) ->String
[Foundation] Returns a string with the given character folding options applied.
Declaration
funcstringByFoldingWithOptions(options:NSStringCompareOptions,locale:NSLocale?) ->String
[Foundation] Returns a new string formed from the String by either
removing characters from the end, or by appending as many
occurrences as necessary of a given pad string.
Declaration
[Foundation] Returns a new string in which all occurrences of a target
string in a specified range of the String are replaced by
another given string.
Declaration
[Foundation] Returns a new string made by replacing in the String
all percent escapes with the matching characters as determined
by a given encoding.
Declaration
funcstringByReplacingPercentEscapesUsingEncoding(encoding:NSStringEncoding) ->String?
[Foundation] Returns a new string made by removing from both ends of
the String characters contained in a given character set.
Declaration
funcstringByTrimmingCharactersInSet(set:NSCharacterSet) ->String
[Foundation] Returns a new string containing the characters of the
String from the one at a given index to the end.
Declaration
funcsubstringFromIndex(index:Index) ->String
[Foundation] Returns a new string containing the characters of the
String up to, but not including, the one at a given index.
Declaration
funcsubstringToIndex(index:Index) ->String
[Foundation] Returns a version of the string with all letters converted to uppercase, taking into account the specified locale.
Declaration
funcuppercaseStringWithLocale(locale:NSLocale?) ->String
Invoke f on the contents of this string, represented as
a nul-terminated array of char, ensuring that the array's
lifetime extends through the execution of f.
Declaration
funcwithCString<Result>(@noescapef:UnsafePointer<Int8>throws->Result)rethrows->Result
Efficiently mutate self by applying body to its characters.
Warning: Do not rely on anything about self (the String
that is the target of this method) during the execution of
body: it may not appear to have its correct value. Instead,
use only the String.CharacterView argument to body.
Declaration
mutatingfuncwithMutableCharacters<R>(body: (inoutString.CharacterView) ->R) ->R
Write a textual representation of self into target.
Declaration
funcwriteTo<Target:OutputStreamType>(inouttarget:Target)
[Foundation] Writes the contents of the String to the URL specified
by url using the specified encoding.
Declaration
funcwriteToURL(url:NSURL,atomicallyuseAuxiliaryFile:Bool,encodingenc:NSStringEncoding)throws
An arbitrary Unicode string value.
Unicode-Correct
Swift strings are designed to be Unicode-correct. In particular, the APIs make it easy to write code that works correctly, and does not surprise end-users, regardless of where you venture in the Unicode character space. For example, the
==operator checks for Unicode canonical equivalence, so two different representations of the same string will always compare equal.Locale-Insensitive
The fundamental operations on Swift strings are not sensitive to locale settings. That's because, for example, the validity of a
Dictionary<String, T>in a running program depends on a given string comparison having a single, stable result. Therefore, Swift always uses the default, un-tailored Unicode algorithms for basic string operations.Importing
Foundationendows swift strings with the full power of theNSStringAPI, which allows you to choose more complex locale-sensitive operations explicitly.Value Semantics
Each string variable,
letbinding, or stored property has an independent value, so mutations to the string are not observable through its copies:Strings use Copy-on-Write so that their data is only copied lazily, upon mutation, when more than one string instance is using the same buffer. Therefore, the first in any sequence of mutating operations may cost
O(N)time and space, whereNis the length of the string's (unspecified) underlying representation.Views
Stringis not itself a collection of anything. Instead, it has properties that present the string's contents as meaningful collections:characters: a collection ofCharacter(extended grapheme cluster) elements, a unit of text that is meaningful to most humans.unicodeScalars: a collection ofUnicodeScalar(Unicode scalar values) the 21-bit codes that are the basic unit of Unicode. These values are equivalent to UTF-32 code units.utf16: a collection ofUTF16.CodeUnit, the 16-bit elements of the string's UTF-16 encoding.utf8: a collection ofUTF8.CodeUnit, the 8-bit elements of the string's UTF-8 encoding.Growth and Capacity
When a string's contiguous storage fills up, new storage must be allocated and characters must be moved to the new storage.
Stringuses an exponential growth strategy that makesappenda constant time operation when amortized over many invocations.Objective-C Bridge
Stringis bridged to Objective-C asNSString, and aStringthat originated in Objective-C may store its characters in anNSString. Since any arbitrary subclass ofNSSStringcan become aString, there are no guarantees about representation or efficiency in this case. SinceNSStringis immutable, it is just as though the storage was shared by some copy: the first in any sequence of mutating operations causes elements to be copied into unique, contiguous storage which may costO(N)time and space, whereNis the length of the string representation (or more, if the underlyingNSStringis has unusual performance characteristics).