Strings and Characters

String Literals

You can include predefined `String` values within your code as *string literals*.
A string literal is a sequence of characters
surrounded by double quotation marks (`"`).

Use a string literal as an initial value for a constant or variable:

```swift
let someString = "Some string literal value"
```

<!--
  - test: `stringLiterals`

  ```swifttest
  -> let someString = "Some string literal value"
  ```
-->

Note that Swift infers a type of `String` for the `someString` constant
because it's initialized with a string literal value.

### Multiline String Literals

If you need a string that spans several lines,
use a multiline string literal ---
a sequence of characters
surrounded by three double quotation marks:

<!--
  Quote comes from "Alice's Adventures in Wonderland",
  which has been public domain as of 1907.
-->

```swift
let quotation = """
The White Rabbit put on his spectacles.  "Where shall I begin,
please your Majesty?" he asked.

"Begin at the beginning," the King said gravely, "and go on
till you come to the end; then stop."
"""
```

<!--
  - test: `multiline-string-literals`

  ```swifttest
  -> let quotation = """
     The White Rabbit put on his spectacles.  "Where shall I begin,
     please your Majesty?" he asked.

     "Begin at the beginning," the King said gravely, "and go on
     till you come to the end; then stop."
     """
  >> let newlines = quotation.filter { $0 == "\n" }
  >> print(newlines.count)
  << 4
  ```
-->

A multiline string literal includes all of the lines between
its opening and closing quotation marks.
The string begins on the first line after the opening quotation marks (`"""`)
and ends on the line before the closing quotation marks,
which means that neither of the strings below
start or end with a line break:

```swift
let singleLineString = "These are the same."
let multilineString = """
These are the same.
"""
```

<!--
  - test: `multiline-string-literals`

  ```swifttest
  -> let singleLineString = "These are the same."
  -> let multilineString = """
     These are the same.
     """
  >> print(singleLineString == multilineString)
  << true
  ```
-->

When your source code includes a line break
inside of a multiline string literal,
that line break also appears in the string's value.
If you want to use line breaks
to make your source code easier to read,
but you don't want the line breaks to be part of the string's value,
write a backslash (`\`) at the end of those lines:

```swift
let softWrappedQuotation = """
The White Rabbit put on his spectacles.  "Where shall I begin, \
please your Majesty?" he asked.

"Begin at the beginning," the King said gravely, "and go on \
till you come to the end; then stop."
"""
```

<!--
  - test: `multiline-string-literals`

  ```swifttest
  -> let softWrappedQuotation = """
     The White Rabbit put on his spectacles.  "Where shall I begin, \
     please your Majesty?" he asked.

     "Begin at the beginning," the King said gravely, "and go on \
     till you come to the end; then stop."
     """
  >> let softNewlines = softWrappedQuotation.filter { $0 == "\n" }
  >> print(softNewlines.count)
  << 2
  ```
-->

To make a multiline string literal that begins or ends with a line feed,
write a blank line as the first or last line.
For example:

```swift
let lineBreaks = """

This string starts with a line break.
It also ends with a line break.

"""
```

<!--
  - test: `multiline-string-literals`

  ```swifttest
  -> let lineBreaks = """

     This string starts with a line break.
     It also ends with a line break.

     """
  ```
-->

<!--
  These are well-fed lines!
-->

A multiline string can be indented to match the surrounding code.
The whitespace before the closing quotation marks (`"""`)
tells Swift what whitespace to ignore before all of the other lines.
However, if you write whitespace at the beginning of a line
in addition to what's before the closing quotation marks,
that whitespace *is* included.

![](multilineStringWhitespace)

<!--
  Using an image here is a little clearer than a code listing,
  since it can call out which spaces "count".
-->

<!--
  - test: `multiline-string-literal-whitespace`

  ```swifttest
  -> let linesWithIndentation = """
         This line doesn't begin with whitespace.
             This line begins with four spaces.
         This line doesn't begin with whitespace.
         """
  ```
-->

In the example above,
even though the entire multiline string literal is indented,
the first and last lines in the string don't begin with any whitespace.
The middle line has more indentation than the closing quotation marks,
so it starts with that extra four-space indentation.

### Special Characters in String Literals

String literals can include the following special characters:

- The escaped special characters `\0` (null character), `\\` (backslash),
  `\t` (horizontal tab), `\n` (line feed), `\r` (carriage return),
  `\"` (double quotation mark) and `\'` (single quotation mark)
- An arbitrary Unicode scalar value, written as `\u{`*n*`}`,
  where *n* is a 1--8 digit hexadecimal number
  (Unicode is discussed in <doc:StringsAndCharacters#Unicode> below)

<!--
  - test: `stringLiteralUnicodeScalar`

  ```swifttest
  >> _ = "\u{0}"
  >> _ = "\u{00000000}"
  >> _ = "\u{000000000}"
  !$ error: \u{...} escape sequence expects between 1 and 8 hex digits
  !! _ = "\u{000000000}"
  !!      ^
  >> _ = "\u{10FFFF}"
  >> _ = "\u{110000}"
  !$ error: invalid unicode scalar
  !! _ = "\u{110000}"
  !!      ^
  ```
-->

The code below shows four examples of these special characters.
The `wiseWords` constant contains two escaped double quotation marks.
The `dollarSign`, `blackHeart`, and `sparklingHeart` constants
demonstrate the Unicode scalar format:

```swift
let wiseWords = "\"Imagination is more important than knowledge\" - Einstein"
// "Imagination is more important than knowledge" - Einstein
let dollarSign = "\u{24}"        // $,  Unicode scalar U+0024
let blackHeart = "\u{2665}"      // ♥,  Unicode scalar U+2665
let sparklingHeart = "\u{1F496}" // 💖, Unicode scalar U+1F496
```

<!--
  - test: `specialCharacters`

  ```swifttest
  -> let wiseWords = "\"Imagination is more important than knowledge\" - Einstein"
  >> print(wiseWords)
  </ "Imagination is more important than knowledge" - Einstein
  -> let dollarSign = "\u{24}"        // $,  Unicode scalar U+0024
  >> assert(dollarSign == "$")
  -> let blackHeart = "\u{2665}"      // ♥,  Unicode scalar U+2665
  >> assert(blackHeart == "♥")
  -> let sparklingHeart = "\u{1F496}" // 💖, Unicode scalar U+1F496
  >> assert(sparklingHeart == "💖")
  ```
-->

Because multiline string literals use three double quotation marks instead of just one,
you can include a double quotation mark (`"`) inside of a multiline string literal
without escaping it.
To include the text `"""` in a multiline string,
escape at least one of the quotation marks.
For example:

```swift
let threeDoubleQuotationMarks = """
Escaping the first quotation mark \"""
Escaping all three quotation marks \"\"\"
"""
```

<!--
  - test: `multiline-string-literals`

  ```swifttest
  -> let threeDoubleQuotationMarks = """
     Escaping the first quotation mark \"""
     Escaping all three quotation marks \"\"\"
     """
  >> print(threeDoubleQuotationMarks)
  << Escaping the first quotation mark """
  << Escaping all three quotation marks """
  ```
-->

### Extended String Delimiters

You can place a string literal within *extended delimiters*
to include special characters in a string
without invoking their effect.
You place your string within quotation marks (`"`)
and surround that with number signs (`#`).
For example, printing the string literal `#"Line 1\nLine 2"#`
prints the line feed escape sequence (`\n`)
rather than printing the string across two lines.

If you need the special effects of a character in a string literal,
match the number of number signs within the string
following the escape character (`\`).
For example, if your string is `#"Line 1\nLine 2"#`
and you want to break the line,
you can use `#"Line 1\#nLine 2"#` instead.
Similarly, `###"Line1\###nLine2"###` also breaks the line.

String literals created using extended delimiters can also be multiline string literals.
You can use extended delimiters to include the text `"""` in a multiline string,
overriding the default behavior that ends the literal. For example:

```swift
let threeMoreDoubleQuotationMarks = #"""
Here are three more double quotes: """
"""#
```

<!--
  - test: `extended-string-delimiters`

  ```swifttest
  -> let threeMoreDoubleQuotationMarks = #"""
     Here are three more double quotes: """
     """#
  >> print(threeMoreDoubleQuotationMarks)
  << Here are three more double quotes: """
  ```
-->

Initializing an Empty String

To create an empty String value as the starting point for building a longer string, either assign an empty string literal to a variable or initialize a new String instance with initializer syntax:

var emptyString = ""               // empty string literal
var anotherEmptyString = String()  // initializer syntax
// these two strings are both empty, and are equivalent to each other

Find out whether a String value is empty by checking its Boolean isEmpty property:

if emptyString.isEmpty {
    print("Nothing to see here")
}
// Prints "Nothing to see here".

String Mutability

You indicate whether a particular String can be modified (or mutated) by assigning it to a variable (in which case it can be modified), or to a constant (in which case it can't be modified):

var variableString = "Horse"
variableString += " and carriage"
// variableString is now "Horse and carriage"

let constantString = "Highlander"
constantString += " and another Highlander"
// this reports a compile-time error - a constant string cannot be modified

Note: This approach is different from string mutation in Objective-C and Cocoa, where you choose between two classes (NSString and NSMutableString) to indicate whether a string can be mutated.

Strings Are Value Types

Swift's String type is a value type. If you create a new String value, that String value is copied when it's passed to a function or method, or when it's assigned to a constant or variable. In each case, a new copy of the existing String value is created, and the new copy is passed or assigned, not the original version. Value types are described in ClassesAndStructures — Structures and Enumerations Are Value Types.

Swift's copy-by-default String behavior ensures that when a function or method passes you a String value, it's clear that you own that exact String value, regardless of where it came from. You can be confident that the string you are passed won't be modified unless you modify it yourself.

Behind the scenes, Swift's compiler optimizes string usage so that actual copying takes place only when absolutely necessary. This means you always get great performance when working with strings as value types.

Working with Characters

You can access the individual Character values for a String by iterating over the string with a for-in loop:

for character in "Dog!🐶" {
    print(character)
}
// D
// o
// g
// !
// 🐶

The for-in loop is described in ControlFlow — For In Loops.

Alternatively, you can create a stand-alone Character constant or variable from a single-character string literal by providing a Character type annotation:

let exclamationMark: Character = "!"

String values can be constructed by passing an array of Character values as an argument to its initializer:

let catCharacters: [Character] = ["C", "a", "t", "!", "🐱"]
let catString = String(catCharacters)
print(catString)
// Prints "Cat!🐱".

Concatenating Strings and Characters

String values can be added together (or concatenated) with the addition operator (+) to create a new String value:

let string1 = "hello"
let string2 = " there"
var welcome = string1 + string2
// welcome now equals "hello there"

You can also append a String value to an existing String variable with the addition assignment operator (+=):

var instruction = "look over"
instruction += string2
// instruction now equals "look over there"

You can append a Character value to a String variable with the String type's append() method:

let exclamationMark: Character = "!"
welcome.append(exclamationMark)
// welcome now equals "hello there!"

Note: You can't append a String or Character to an existing Character variable, because a Character value must contain a single character only.

If you're using multiline string literals to build up the lines of a longer string, you want every line in the string to end with a line break, including the last line. For example:

let badStart = """
    one
    two
    """
let end = """
    three
    """
print(badStart + end)
// Prints two lines:
// one
// twothree

let goodStart = """
    one
    two

    """
print(goodStart + end)
// Prints three lines:
// one
// two
// three

In the code above, concatenating badStart with end produces a two-line string, which isn't the desired result. Because the last line of badStart doesn't end with a line break, that line gets combined with the first line of end. In contrast, both lines of goodStart end with a line break, so when it's combined with end the result has three lines, as expected.

String Interpolation

String interpolation is a way to construct a new String value from a mix of constants, variables, literals, and expressions by including their values inside a string literal. You can use string interpolation in both single-line and multiline string literals. Each item that you insert into the string literal is wrapped in a pair of parentheses, prefixed by a backslash (\):

let multiplier = 3
let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)"
// message is "3 times 2.5 is 7.5"

In the example above, the value of multiplier is inserted into a string literal as \(multiplier). This placeholder is replaced with the actual value of multiplier when the string interpolation is evaluated to create an actual string.

The value of multiplier is also part of a larger expression later in the string. This expression calculates the value of Double(multiplier) 2.5 and inserts the result (7.5) into the string. In this case, the expression is written as \(Double(multiplier) 2.5) when it's included inside the string literal.

You can use extended string delimiters to create strings containing characters that would otherwise be treated as a string interpolation. For example:

print(#"Write an interpolated string in Swift using \(multiplier)."#)
// Prints "Write an interpolated string in Swift using \(multiplier)."

To use string interpolation inside a string that uses extended delimiters, match the number of number signs after the backslash to the number of number signs at the beginning and end of the string. For example:

print(#"6 times 7 is \#(6 * 7)."#)
// Prints "6 times 7 is 42."

Note: The expressions you write inside parentheses within an interpolated string can't contain an unescaped backslash (\), a carriage return, or a line feed. However, they can contain other string literals.

Unicode

Unicode is an international standard for encoding, representing, and processing text in different writing systems. It enables you to represent almost any character from any language in a standardized form, and to read and write those characters to and from an external source such as a text file or web page. Swift's String and Character types are fully Unicode-compliant, as described in this section.

Unicode Scalar Values

Behind the scenes, Swift's native String type is built from Unicode scalar values. A Unicode scalar value is a unique 21-bit number for a character or modifier, such as U+0061 for LATIN SMALL LETTER A ("a"), or U+1F425 for FRONT-FACING BABY CHICK ("🐥").

Note that not all 21-bit Unicode scalar values are assigned to a character --- some scalars are reserved for future assignment or for use in UTF-16 encoding. Scalar values that have been assigned to a character typically also have a name, such as LATIN SMALL LETTER A and FRONT-FACING BABY CHICK in the examples above.

Extended Grapheme Clusters

Every instance of Swift's Character type represents a single extended grapheme cluster. An extended grapheme cluster is a sequence of one or more Unicode scalars that (when combined) produce a single human-readable character.

Here's an example. The letter é can be represented as the single Unicode scalar é (LATIN SMALL LETTER E WITH ACUTE, or U+00E9). However, the same letter can also be represented as a pair of scalars --- a standard letter e (LATIN SMALL LETTER E, or U+0065), followed by the COMBINING ACUTE ACCENT scalar (U+0301). The COMBINING ACUTE ACCENT scalar is graphically applied to the scalar that precedes it, turning an e into an é when it's rendered by a Unicode-aware text-rendering system.

In both cases, the letter é is represented as a single Swift Character value that represents an extended grapheme cluster. In the first case, the cluster contains a single scalar; in the second case, it's a cluster of two scalars:

let eAcute: Character = "\u{E9}"                         // é
let combinedEAcute: Character = "\u{65}\u{301}"          // e followed by ́
// eAcute is é, combinedEAcute is é

Extended grapheme clusters are a flexible way to represent many complex script characters as a single Character value. For example, Hangul syllables from the Korean alphabet can be represented as either a precomposed or decomposed sequence. Both of these representations qualify as a single Character value in Swift:

let precomposed: Character = "\u{D55C}"                  // 한
let decomposed: Character = "\u{1112}\u{1161}\u{11AB}"   // ᄒ, ᅡ, ᆫ
// precomposed is 한, decomposed is 한

Extended grapheme clusters enable scalars for enclosing marks (such as COMBINING ENCLOSING CIRCLE, or U+20DD) to enclose other Unicode scalars as part of a single Character value:

let enclosedEAcute: Character = "\u{E9}\u{20DD}"
// enclosedEAcute is é⃝

Unicode scalars for regional indicator symbols can be combined in pairs to make a single Character value, such as this combination of REGIONAL INDICATOR SYMBOL LETTER U (U+1F1FA) and REGIONAL INDICATOR SYMBOL LETTER S (U+1F1F8):

let regionalIndicatorForUS: Character = "\u{1F1FA}\u{1F1F8}"
// regionalIndicatorForUS is 🇺🇸

Counting Characters

To retrieve a count of the Character values in a string, use the count property of the string:

let unusualMenagerie = "Koala 🐨, Snail 🐌, Penguin 🐧, Dromedary 🐪"
print("unusualMenagerie has \(unusualMenagerie.count) characters")
// Prints "unusualMenagerie has 40 characters".

Note that Swift's use of extended grapheme clusters for Character values means that string concatenation and modification may not always affect a string's character count.

For example, if you initialize a new string with the four-character word cafe, and then append a COMBINING ACUTE ACCENT (U+0301) to the end of the string, the resulting string will still have a character count of 4, with a fourth character of é, not e:

var word = "cafe"
print("the number of characters in \(word) is \(word.count)")
// Prints "the number of characters in cafe is 4".

word += "\u{301}"    // COMBINING ACUTE ACCENT, U+0301

print("the number of characters in \(word) is \(word.count)")
// Prints "the number of characters in café is 4".

Note: Extended grapheme clusters can be composed of multiple Unicode scalars. This means that different characters --- and different representations of the same character --- can require different amounts of memory to store. Because of this, characters in Swift don't each take up the same amount of memory within a string's representation. As a result, the number of characters in a string can't be calculated without iterating through the string to determine its extended grapheme cluster boundaries. If you are working with particularly long string values, be aware that the count property must iterate over the Unicode scalars in the entire string in order to determine the characters for that string.

The count of the characters returned by the count property isn't always the same as the length property of an NSString that contains the same characters. The length of an NSString is based on the number of 16-bit code units within the string's UTF-16 representation and not the number of Unicode extended grapheme clusters within the string.

Accessing and Modifying a String

You access and modify a string through its methods and properties, or by using subscript syntax.

String Indices

Each String value has an associated index type, String.Index, which corresponds to the position of each Character in the string.

As mentioned above, different characters can require different amounts of memory to store, so in order to determine which Character is at a particular position, you must iterate over each Unicode scalar from the start or end of that String. For this reason, Swift strings can't be indexed by integer values.

Use the startIndex property to access the position of the first Character of a String. The endIndex property is the position after the last character in a String. As a result, the endIndex property isn't a valid argument to a string's subscript. If a String is empty, startIndex and endIndex are equal.

You access the indices before and after a given index using the index(before:) and index(after:) methods of String. To access an index farther away from the given index, you can use the index(_:offsetBy:) method instead of calling one of these methods multiple times.

You can use subscript syntax to access the Character at a particular String index.

let greeting = "Guten Tag!"
greeting[greeting.startIndex]
// G
greeting[greeting.index(before: greeting.endIndex)]
// !
greeting[greeting.index(after: greeting.startIndex)]
// u
let index = greeting.index(greeting.startIndex, offsetBy: 7)
greeting[index]
// a

Attempting to access an index outside of a string's range or a Character at an index outside of a string's range will trigger a runtime error.

greeting[greeting.endIndex] // Error
greeting.index(after: greeting.endIndex) // Error

Use the indices property to access all of the indices of individual characters in a string.

for index in greeting.indices {
    print("\(greeting[index]) ", terminator: "")
}
// Prints "G u t e n   T a g ! ".

Note: You can use the startIndex and endIndex properties and the index(before:), index(after:), and index(_:offsetBy:) methods on any type that conforms to the Collection protocol. This includes String, as shown here, as well as collection types such as Array, Dictionary, and Set.

Inserting and Removing

To insert a single character into a string at a specified index, use the insert(_:at:) method, and to insert the contents of another string at a specified index, use the insert(contentsOf:at:) method.

var welcome = "hello"
welcome.insert("!", at: welcome.endIndex)
// welcome now equals "hello!"

welcome.insert(contentsOf: " there", at: welcome.index(before: welcome.endIndex))
// welcome now equals "hello there!"

To remove a single character from a string at a specified index, use the remove(at:) method, and to remove a substring at a specified range, use the removeSubrange(_:) method:

welcome.remove(at: welcome.index(before: welcome.endIndex))
// welcome now equals "hello there"

let range = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex
welcome.removeSubrange(range)
// welcome now equals "hello"

Note: You can use the insert(:at:), insert(contentsOf:at:), remove(at:), and removeSubrange(:) methods on any type that conforms to the RangeReplaceableCollection protocol. This includes String, as shown here, as well as collection types such as Array, Dictionary, and Set.

Substrings

When you get a substring from a string --- for example, using a subscript or a method like prefix(_:) --- the result is an instance of Substring, not another string. Substrings in Swift have most of the same methods as strings, which means you can work with substrings the same way you work with strings. However, unlike strings, you use substrings for only a short amount of time while performing actions on a string. When you're ready to store the result for a longer time, you convert the substring to an instance of String. For example:

let greeting = "Hello, world!"
let index = greeting.firstIndex(of: ",") ?? greeting.endIndex
let beginning = greeting[..<index]
// beginning is "Hello"

// Convert the result to a String for long-term storage.
let newString = String(beginning)

Like strings, each substring has a region of memory where the characters that make up the substring are stored. The difference between strings and substrings is that, as a performance optimization, a substring can reuse part of the memory that's used to store the original string, or part of the memory that's used to store another substring. (Strings have a similar optimization, but if two strings share memory, they're equal.) This performance optimization means you don't have to pay the performance cost of copying memory until you modify either the string or substring. As mentioned above, substrings aren't suitable for long-term storage --- because they reuse the storage of the original string, the entire original string must be kept in memory as long as any of its substrings are being used.

In the example above, greeting is a string, which means it has a region of memory where the characters that make up the string are stored. Because beginning is a substring of greeting, it reuses the memory that greeting uses. In contrast, newString is a string --- when it's created from the substring, it has its own storage. The figure below shows these relationships:

Note: Both String and Substring conform to the StringProtocol protocol, which means it's often convenient for string-manipulation functions to accept a StringProtocol value. You can call such functions with either a String or Substring value.

Comparing Strings

Swift provides three ways to compare textual values:
string and character equality, prefix equality, and suffix equality.

### String and Character Equality

String and character equality is checked with the “equal to” operator (`==`)
and the “not equal to” operator (`!=`),
as described in <doc:BasicOperators#Comparison-Operators>:

```swift
let quotation = "We're a lot alike, you and I."
let sameQuotation = "We're a lot alike, you and I."
if quotation == sameQuotation {
    print("These two strings are considered equal")
}
// Prints "These two strings are considered equal".
```

<!--
  - test: `stringEquality`

  ```swifttest
  -> let quotation = "We're a lot alike, you and I."
  -> let sameQuotation = "We're a lot alike, you and I."
  -> if quotation == sameQuotation {
        print("These two strings are considered equal")
     }
  <- These two strings are considered equal
  ```
-->

Two `String` values (or two `Character` values) are considered equal if
their extended grapheme clusters are *canonically equivalent*.
Extended grapheme clusters are canonically equivalent if they have
the same linguistic meaning and appearance,
even if they're composed from different Unicode scalars behind the scenes.

<!--
  - test: `characterComparisonUsesCanonicalEquivalence`

  ```swifttest
  -> let eAcute: Character = "\u{E9}"
  -> let combinedEAcute: Character = "\u{65}\u{301}"
  -> if eAcute != combinedEAcute {
        print("not equivalent, which isn't expected")
     } else {
        print("equivalent, as expected")
     }
  <- equivalent, as expected
  ```
-->

<!--
  - test: `stringComparisonUsesCanonicalEquivalence`

  ```swifttest
  -> let cafe1 = "caf\u{E9}"
  -> let cafe2 = "caf\u{65}\u{301}"
  -> if cafe1 != cafe2 {
        print("not equivalent, which isn't expected")
     } else {
        print("equivalent, as expected")
     }
  <- equivalent, as expected
  ```
-->

For example, `LATIN SMALL LETTER E WITH ACUTE` (`U+00E9`)
is canonically equivalent to `LATIN SMALL LETTER E` (`U+0065`)
followed by `COMBINING ACUTE ACCENT` (`U+0301`).
Both of these extended grapheme clusters are valid ways to represent the character `é`,
and so they're considered to be canonically equivalent:

```swift
// "Voulez-vous un café?" using LATIN SMALL LETTER E WITH ACUTE
let eAcuteQuestion = "Voulez-vous un caf\u{E9}?"

// "Voulez-vous un café?" using LATIN SMALL LETTER E and COMBINING ACUTE ACCENT
let combinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?"

if eAcuteQuestion == combinedEAcuteQuestion {
    print("These two strings are considered equal")
}
// Prints "These two strings are considered equal".
```

<!--
  - test: `stringEquality`

  ```swifttest
  // "Voulez-vous un café?" using LATIN SMALL LETTER E WITH ACUTE
  -> let eAcuteQuestion = "Voulez-vous un caf\u{E9}?"

  // "Voulez-vous un café?" using LATIN SMALL LETTER E and COMBINING ACUTE ACCENT
  -> let combinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?"

  -> if eAcuteQuestion == combinedEAcuteQuestion {
        print("These two strings are considered equal")
     }
  <- These two strings are considered equal
  ```
-->

Conversely, `LATIN CAPITAL LETTER A` (`U+0041`, or `"A"`),
as used in English, is *not* equivalent to
`CYRILLIC CAPITAL LETTER A` (`U+0410`, or `"А"`),
as used in Russian.
The characters are visually similar,
but don't have the same linguistic meaning:

```swift
let latinCapitalLetterA: Character = "\u{41}"

let cyrillicCapitalLetterA: Character = "\u{0410}"

if latinCapitalLetterA != cyrillicCapitalLetterA {
    print("These two characters aren't equivalent.")
}
// Prints "These two characters aren't equivalent."
```

<!--
  - test: `stringEquality`

  ```swifttest
  -> let latinCapitalLetterA: Character = "\u{41}"
  >> assert(latinCapitalLetterA == "A")

  -> let cyrillicCapitalLetterA: Character = "\u{0410}"
  >> assert(cyrillicCapitalLetterA == "А")

  -> if latinCapitalLetterA != cyrillicCapitalLetterA {
        print("These two characters aren't equivalent.")
     }
  <- These two characters aren't equivalent.
  ```
-->

> Note: String and character comparisons in Swift aren't locale-sensitive.

<!--
  TODO: Add a cross reference to NSString.localizedCompare and
  NSString.localizedCaseInsensitiveCompare.  See also
  https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Strings/Articles/SearchingStrings.html#//apple_ref/doc/uid/20000149-SW4
-->

### Prefix and Suffix Equality

To check whether a string has a particular string prefix or suffix,
call the string's `hasPrefix(_:)` and `hasSuffix(_:)` methods,
both of which take a single argument of type `String` and return a Boolean value.

<!--
  - test: `prefixComparisonUsesCharactersNotScalars`

  ```swifttest
  -> let ecole = "\u{E9}cole"
  -> if ecole.hasPrefix("\u{E9}") {
        print("Has U+00E9 prefix, as expected.")
     } else {
        print("Does not have U+00E9 prefix, which is unexpected.")
     }
  <- Has U+00E9 prefix, as expected.
  -> if ecole.hasPrefix("\u{65}\u{301}") {
        print("Has U+0065 U+0301 prefix, as expected.")
     } else {
        print("Does not have U+0065 U+0301 prefix, which is unexpected.")
     }
  <- Has U+0065 U+0301 prefix, as expected.
  ```
-->

<!--
  - test: `suffixComparisonUsesCharactersNotScalars`

  ```swifttest
  -> let cafe = "caf\u{E9}"
  -> if cafe.hasSuffix("\u{E9}") {
        print("Has U+00E9 suffix, as expected.")
     } else {
        print("Does not have U+00E9 suffix, which is unexpected.")
     }
  <- Has U+00E9 suffix, as expected.
  -> if cafe.hasSuffix("\u{65}\u{301}") {
        print("Has U+0065 U+0301 suffix, as expected.")
     } else {
        print("Does not have U+0065 U+0301 suffix, which is unexpected.")
     }
  <- Has U+0065 U+0301 suffix, as expected.
  ```
-->

The examples below consider an array of strings representing
the scene locations from the first two acts of Shakespeare's *Romeo and Juliet*:

```swift
let romeoAndJuliet = [
    "Act 1 Scene 1: Verona, A public place",
    "Act 1 Scene 2: Capulet's mansion",
    "Act 1 Scene 3: A room in Capulet's mansion",
    "Act 1 Scene 4: A street outside Capulet's mansion",
    "Act 1 Scene 5: The Great Hall in Capulet's mansion",
    "Act 2 Scene 1: Outside Capulet's mansion",
    "Act 2 Scene 2: Capulet's orchard",
    "Act 2 Scene 3: Outside Friar Lawrence's cell",
    "Act 2 Scene 4: A street in Verona",
    "Act 2 Scene 5: Capulet's mansion",
    "Act 2 Scene 6: Friar Lawrence's cell"
]
```

<!--
  - test: `prefixesAndSuffixes`

  ```swifttest
  -> let romeoAndJuliet = [
        "Act 1 Scene 1: Verona, A public place",
        "Act 1 Scene 2: Capulet's mansion",
        "Act 1 Scene 3: A room in Capulet's mansion",
        "Act 1 Scene 4: A street outside Capulet's mansion",
        "Act 1 Scene 5: The Great Hall in Capulet's mansion",
        "Act 2 Scene 1: Outside Capulet's mansion",
        "Act 2 Scene 2: Capulet's orchard",
        "Act 2 Scene 3: Outside Friar Lawrence's cell",
        "Act 2 Scene 4: A street in Verona",
        "Act 2 Scene 5: Capulet's mansion",
        "Act 2 Scene 6: Friar Lawrence's cell"
     ]
  ```
-->

You can use the `hasPrefix(_:)` method with the `romeoAndJuliet` array
to count the number of scenes in Act 1 of the play:

```swift
var act1SceneCount = 0
for scene in romeoAndJuliet {
    if scene.hasPrefix("Act 1 ") {
        act1SceneCount += 1
    }
}
print("There are \(act1SceneCount) scenes in Act 1")
// Prints "There are 5 scenes in Act 1".
```

<!--
  - test: `prefixesAndSuffixes`

  ```swifttest
  -> var act1SceneCount = 0
  -> for scene in romeoAndJuliet {
        if scene.hasPrefix("Act 1 ") {
           act1SceneCount += 1
        }
     }
  -> print("There are \(act1SceneCount) scenes in Act 1")
  <- There are 5 scenes in Act 1
  ```
-->

Similarly, use the `hasSuffix(_:)` method to count the number of scenes
that take place in or around Capulet's mansion and Friar Lawrence's cell:

```swift
var mansionCount = 0
var cellCount = 0
for scene in romeoAndJuliet {
    if scene.hasSuffix("Capulet's mansion") {
        mansionCount += 1
    } else if scene.hasSuffix("Friar Lawrence's cell") {
        cellCount += 1
    }
}
print("\(mansionCount) mansion scenes; \(cellCount) cell scenes")
// Prints "6 mansion scenes; 2 cell scenes".
```

<!--
  - test: `prefixesAndSuffixes`

  ```swifttest
  -> var mansionCount = 0
  -> var cellCount = 0
  -> for scene in romeoAndJuliet {
        if scene.hasSuffix("Capulet's mansion") {
           mansionCount += 1
        } else if scene.hasSuffix("Friar Lawrence's cell") {
           cellCount += 1
        }
     }
  -> print("\(mansionCount) mansion scenes; \(cellCount) cell scenes")
  <- 6 mansion scenes; 2 cell scenes
  ```
-->

> Note: The `hasPrefix(_:)` and `hasSuffix(_:)` methods
> perform a character-by-character canonical equivalence comparison between
> the extended grapheme clusters in each string,
> as described in <doc:StringsAndCharacters#String-and-Character-Equality>.

Unicode Representations of Strings

When a Unicode string is written to a text file or some other storage,
the Unicode scalars in that string are encoded in one of
several Unicode-defined *encoding forms*.
Each form encodes the string in small chunks known as *code units*.
These include the UTF-8 encoding form (which encodes a string as 8-bit code units),
the UTF-16 encoding form (which encodes a string as 16-bit code units),
and the UTF-32 encoding form (which encodes a string as 32-bit code units).

Swift provides several different ways to access Unicode representations of strings.
You can iterate over the string with a `for`-`in` statement,
to access its individual `Character` values as Unicode extended grapheme clusters.
This process is described in <doc:StringsAndCharacters#Working-with-Characters>.

Alternatively, access a `String` value
in one of three other Unicode-compliant representations:

- A collection of UTF-8 code units (accessed with the string's `utf8` property)
- A collection of UTF-16 code units (accessed with the string's `utf16` property)
- A collection of 21-bit Unicode scalar values,
  equivalent to the string's UTF-32 encoding form
  (accessed with the string's `unicodeScalars` property)

Each example below shows a different representation of the following string,
which is made up of the characters `D`, `o`, `g`,
`‼` (`DOUBLE EXCLAMATION MARK`, or Unicode scalar `U+203C`),
and the 🐶 character (`DOG FACE`, or Unicode scalar `U+1F436`):

```swift
let dogString = "Dog‼🐶"
```

<!--
  - test: `unicodeRepresentations`

  ```swifttest
  -> let dogString = "Dog‼🐶"
  ```
-->

### UTF-8 Representation

You can access a UTF-8 representation of a `String`
by iterating over its `utf8` property.
This property is of type `String.UTF8View`,
which is a collection of unsigned 8-bit (`UInt8`) values,
one for each byte in the string's UTF-8 representation:

![](UTF8)

```swift
for codeUnit in dogString.utf8 {
    print("\(codeUnit) ", terminator: "")
}
print("")
// Prints "68 111 103 226 128 188 240 159 144 182 ".
```

<!--
  - test: `unicodeRepresentations`

  ```swifttest
  -> for codeUnit in dogString.utf8 {
        print("\(codeUnit) ", terminator: "")
     }
  -> print("")
  << 68 111 103 226 128 188 240 159 144 182
  // Prints "68 111 103 226 128 188 240 159 144 182 ".
  ```
-->

<!--
  Workaround for rdar://26016325
-->

In the example above, the first three decimal `codeUnit` values
(`68`, `111`, `103`)
represent the characters `D`, `o`, and `g`,
whose UTF-8 representation is the same as their ASCII representation.
The next three decimal `codeUnit` values
(`226`, `128`, `188`)
are a three-byte UTF-8 representation of the `DOUBLE EXCLAMATION MARK` character.
The last four `codeUnit` values (`240`, `159`, `144`, `182`)
are a four-byte UTF-8 representation of the `DOG FACE` character.

<!--
  TODO: contiguousUTF8()
-->

<!--
  TODO: nulTerminatedUTF8()
  (which returns a NativeArray, but handwave this for now)
-->

### UTF-16 Representation

You can access a UTF-16 representation of a `String`
by iterating over its `utf16` property.
This property is of type `String.UTF16View`,
which is a collection of unsigned 16-bit (`UInt16`) values,
one for each 16-bit code unit in the string's UTF-16 representation:

![](UTF16)

```swift
for codeUnit in dogString.utf16 {
    print("\(codeUnit) ", terminator: "")
}
print("")
// Prints "68 111 103 8252 55357 56374 ".
```

<!--
  - test: `unicodeRepresentations`

  ```swifttest
  -> for codeUnit in dogString.utf16 {
        print("\(codeUnit) ", terminator: "")
     }
  -> print("")
  << 68 111 103 8252 55357 56374
  // Prints "68 111 103 8252 55357 56374 ".
  ```
-->

<!--
  Workaround for rdar://26016325
-->

Again, the first three `codeUnit` values
(`68`, `111`, `103`)
represent the characters `D`, `o`, and `g`,
whose UTF-16 code units have the same values as in the string's UTF-8 representation
(because these Unicode scalars represent ASCII characters).

The fourth `codeUnit` value (`8252`) is a decimal equivalent of
the hexadecimal value `203C`,
which represents the Unicode scalar `U+203C`
for the `DOUBLE EXCLAMATION MARK` character.
This character can be represented as a single code unit in UTF-16.

The fifth and sixth `codeUnit` values (`55357` and `56374`)
are a UTF-16 surrogate pair representation of the `DOG FACE` character.
These values are a high-surrogate value of `U+D83D` (decimal value `55357`)
and a low-surrogate value of `U+DC36` (decimal value `56374`).

### Unicode Scalar Representation

You can access a Unicode scalar representation of a `String` value
by iterating over its `unicodeScalars` property.
This property is of type `UnicodeScalarView`,
which is a collection of values of type `UnicodeScalar`.

Each `UnicodeScalar` has a `value` property that returns
the scalar's 21-bit value, represented within a `UInt32` value:

![](UnicodeScalar)

```swift
for scalar in dogString.unicodeScalars {
    print("\(scalar.value) ", terminator: "")
}
print("")
// Prints "68 111 103 8252 128054 ".
```

<!--
  - test: `unicodeRepresentations`

  ```swifttest
  -> for scalar in dogString.unicodeScalars {
        print("\(scalar.value) ", terminator: "")
     }
  -> print("")
  << 68 111 103 8252 128054
  // Prints "68 111 103 8252 128054 ".
  ```
-->

<!--
  Workaround for rdar://26016325
-->

The `value` properties for the first three `UnicodeScalar` values
(`68`, `111`, `103`)
once again represent the characters `D`, `o`, and `g`.

The fourth `codeUnit` value (`8252`) is again a decimal equivalent of
the hexadecimal value `203C`,
which represents the Unicode scalar `U+203C`
for the `DOUBLE EXCLAMATION MARK` character.

The `value` property of the fifth and final `UnicodeScalar`, `128054`,
is a decimal equivalent of the hexadecimal value `1F436`,
which represents the Unicode scalar `U+1F436` for the `DOG FACE` character.

As an alternative to querying their `value` properties,
each `UnicodeScalar` value can also be used to construct a new `String` value,
such as with string interpolation:

```swift
for scalar in dogString.unicodeScalars {
    print("\(scalar) ")
}
// D
// o
// g
// ‼
// 🐶
```

<!--
  - test: `unicodeRepresentations`

  ```swifttest
  -> for scalar in dogString.unicodeScalars {
        print("\(scalar) ")
     }
  </ D
  </ o
  </ g
  </ ‼
  </ 🐶
  ```
-->

<!--
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Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
Licensed under Apache License v2.0 with Runtime Library Exception

See https://swift.org/LICENSE.txt for license information
See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-->