Arrays are one of Swift's three primary collection types.
An array is an ordered list of elements.
Arrays can store elements of any type, but all elements in a given array must share the same type.
Arrays are mutable when assigned to a variable, meaning you can add, remove, or modify elements after creating the array.
When assigned to a constant, an array is immutable, meaning its contents cannot be changed.
Array literals are written as a comma-separated list of elements enclosed in square brackets ([...]).
Swift can infer the array's type from the elements inside the literal.
let evenInts = [2, 4, 6, 8, 10, 12]
var oddInts = [1, 3, 5, 7, 9, 11, 13]
let greetings = ["Hello!", "Hi!", "¡Hola!"]
You can also specify the type explicitly.
Array types can be written in two ways: Array<T> or the shorthand syntax [T], where T is the type of values the array contains.
let evenInts: Array<Int> = [2, 4, 6, 8, 10, 12]
var oddInts: [Int] = [1, 3, 5, 7, 9, 11, 13]
let greetings: [String] = ["Hello!", "Hi!", "¡Hola!"]
Size of an Array
You can find the number of elements in an array using its count property:
evenInts.count
// returns 6
Empty Arrays
To create an empty array, you must specify its type.
You can do this using array initializer syntax or an explicit type annotation:
let emptyArray = [Int]()
let emptyArray2 = Array<Int>()
let emptyArray3: [Int] = []
Multi-dimensional Arrays
Arrays can be nested to create multi-dimensional arrays.
When specifying the type of a nested array explicitly, wrap the element type in nested brackets, such as [[Int]] or Array<Array<Int>>:
let multiDimArray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
let multiDimArray2: [[Int]] = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Appending to an Array
You can add an element to the end of a mutable array using the append(_:) method:
var oddInts = [1, 3, 5, 7, 9, 11, 13]
oddInts.append(15)
// oddInts is now [1, 3, 5, 7, 9, 11, 13, 15]
Inserting into an Array
You can insert an element at a specific index using the insert(_:at:) method.
This method takes two arguments: the element to insert and the index at which to insert it.
var oddInts = [1, 3, 5, 7, 9, 11, 13]
oddInts.insert(0, at: 0)
// oddInts is now [0, 1, 3, 5, 7, 9, 11, 13]
Adding Arrays Together
You can combine two arrays into a single array using the + operator.
The + operator creates and returns a new array; it does not modify the original arrays.
var oddInts = [1, 3, 5, 7, 9, 11, 13]
let combined = oddInts + [15, 17, 19]
// combined is [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
print(oddInts)
// prints [1, 3, 5, 7, 9, 11, 13]
Accessing Elements of an Array
You can access an individual element of an array by placing its index inside square brackets ([]) following the array name.
Array indices are zero-based Int values, starting at 0 for the first element.
Accessing an index outside the valid range causes a runtime error and crashes the program.
let evenInts = [2, 4, 6, 8, 10, 12]
let oddInts = [1, 3, 5, 7, 9, 11, 13]
evenInts[2]
// returns 6
oddInts[7]
// Fatal error: Index out of range
Modifying Elements of an Array
You can change an element in a mutable array by assigning a new value to a specific index.
As with reading elements, using an index outside the valid range causes a runtime error.
var evenInts = [2, 4, 6, 8, 10, 12]
evenInts[2] = 0
// evenInts is now [2, 4, 0, 8, 10, 12]
Converting an Array to a String and Back
You can join an array of strings into a single string using the joined(separator:) method, which takes a separator string:
let evenInts = ["2", "4", "6", "8", "10", "12"]
let evenIntsString = evenInts.joined(separator: ", ")
// returns "2, 4, 6, 8, 10, 12"
You can split a string into an array of substrings using the split(separator:) method, passing the delimiter character:
let evenIntsString = "2, 4, 6, 8, 10, 12"
let evenInts = evenIntsString.split(separator: ",")
// returns ["2", " 4", " 6", " 8", " 10", " 12"]
Removing Elements from an Array
You can remove an element at a given index using the remove(at:) method.
The index must be within the array's valid bounds; otherwise, a runtime error occurs.
var oddInts = [1, 3, 5, 7, 9, 11, 13]
oddInts.remove(at: 3)
// oddInts is now [1, 3, 5, 9, 11, 13]
To remove the final element of an array, use the removeLast() method.
Calling removeLast() on an empty array causes a runtime error.
var oddInts = [1, 3, 5, 7, 9, 11, 13]
oddInts.removeLast()
// oddInts is now [1, 3, 5, 7, 9, 11]
Learning Exercise
