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A string represents textual data. In Swift, a String is an ordered collection of Character values, where each character represents a Unicode character.

You create a string using a string literal, which is a sequence of characters surrounded by double quotation marks ("). For multi-line strings, use three double quotation marks ("""):

let hello: String = "Hello, World!"

let poem: String = """
Roses are red,
Violets are blue.
Sugar is sweet,
And so are you.
"""

Swift strings bridge seamlessly with the Foundation framework's NSString class, providing access to extensive text-processing capabilities.

Characters

A Character represents a single extended grapheme cluster—a human-readable character composed of one or more Unicode scalar values. A Unicode scalar value is a 21-bit code point in the range U+0000 to U+D7FF inclusive or U+E000 to U+10FFFF inclusive.

let aChar: Character = "A"

Type Inference

When you write a string literal, Swift automatically infers its type as String. To store a single character as a Character, you must provide an explicit type annotation:

let aString = "A"        // Inferred as String
let aChar: Character = "A" // Explicitly typed as Character
print(type(of: aString)) // Prints String
print(type(of: aChar))   // Prints Character

// The following code will not compile:
let badChar: Character = "Too many characters"
// Error: Cannot convert value of type 'String' to specified type 'Character'

Concatenation

You can join strings together using the addition operator (+):

print("honey" + "comb")
// Prints "honeycomb"

You cannot directly concatenate a Character to a String using + without first converting the character to a string. However, you can use the append(_:) method to append either a string or a character directly to a mutable string:

var greeting = "Hello"
let world = ", world"
let period: Character = "."

greeting.append(world)
print(greeting) // Prints "Hello, world"

greeting.append(period)
print(greeting) // Prints "Hello, world."

String Interpolation

String interpolation allows you to construct a string by embedding constants, variables, literals, and expressions inside string literals. Wrap each expression in parentheses preceded by a backslash (\( ... )):

let radius = 5.0
let circle = "The area of a circle with radius \(radius) is \(Double.pi * radius * radius)"
print(circle) // Prints "The area of a circle with radius 5.0 is 78.53981633974483"

String and Character Properties

Strings and characters offer several properties to inspect their content.

String Properties

Common string properties include:

For a complete list of properties, see the Apple String documentation.

Character Properties

Common character properties include:

For a complete list of properties, see the Apple Character documentation.

Type Conversion

You can convert other types into strings by using the String(_:) initializer, which supports standard types like Int, Double, and Character:

let charX: Character = "x"
print(String(charX))     // Prints "x"
print(String(110))       // Prints "110"
print(String(Double.pi)) // Prints "3.141592653589793"

Special Characters

Swift string literals support several escape sequences for special characters:

let quote: String = "\"Hello\", he said."
print(quote) // Prints "Hello", he said.

let unicode: Character = "\u{1F496}"
print(unicode) // Prints 💖