Swift Language Basics of Arrays

Download Swift Language for free

Example

Array is an ordered collection type in the Swift standard library. It provides O(1) random access and dynamic reallocation. Array is a generic type, so the type of values it contains are known at compile time.

As Array is a value type, its mutability is defined by whether it is annotated as a var (mutable) or let (immutable).

The type [Int] (meaning: an array containing Ints) is syntactic sugar for Array<T>.

Read more about arrays in The Swift Programming Language.

Empty arrays

The following three declarations are equivalent:

// A mutable array of Strings, initially empty.

var arrayOfStrings: [String] = []      // type annotation + array literal
var arrayOfStrings = [String]()        // invoking the [String] initializer
var arrayOfStrings = Array<String>()   // without syntactic sugar

Array literals

An array literal is written with square brackets surrounding comma-separated elements:

// Create an immutable array of type [Int] containing 2, 4, and 7
let arrayOfInts = [2, 4, 7]

The compiler can usually infer the type of an array based on the elements in the literal, but explicit type annotations can override the default:

let arrayOfUInt8s: [UInt8] = [2, 4, 7]   // type annotation on the variable
let arrayOfUInt8s = [2, 4, 7] as [UInt8] // type annotation on the initializer expression
let arrayOfUInt8s = [2 as UInt8, 4, 7]   // explicit for one element, inferred for the others

Arrays with repeated values

// An immutable array of type [String], containing ["Example", "Example", "Example"]
let arrayOfStrings = Array(repeating: "Example",count: 3)

Creating arrays from other sequences

let dictionary = ["foo" : 4, "bar" : 6]

// An immutable array of type [(String, Int)], containing [("bar", 6), ("foo", 4)]
let arrayOfKeyValuePairs = Array(dictionary)

Multi-dimensional arrays

In Swift, a multidimensional array is created by nesting arrays: a 2-dimensional array of Int is [[Int]] (or Array<Array<Int>>).

let array2x3 = [
    [1, 2, 3],
    [4, 5, 6]
]
// array2x3[0][1] is 2, and array2x3[1][2] is 6.

To create a multidimensional array of repeated values, use nested calls of the array initializer:

var array3x4x5 = Array(repeating: Array(repeating: Array(repeating: 0,count: 5),count: 4),count: 3)
Accessing Array Values