Swift Tutorial - Swift Arrays

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To organize a list of variables, we can use arrays.

All items in an array must be of the same type.

Example

The following code shows two ways to create empty arrays that you can add items to later.

var a1:Array<String> = Array<String>()
var a2:[String] = [String]()

The first line shows the long way of declaring an array.

You must use the Array keyword and include the type that is stored in the array between <>.

a1 is an array that can hold a list of strings.

You must also use the assignment operator = to initialize the array followed by the word Array along with the type between <> signs.

The second line is a shorthand method for creating arrays.

We can also use array items to initially create the array.

Swift supports type inference, and you can omit the initialization and the type declaration as follows.

var a3 = ["A", "B", "C"]

Array Mutability

We can add, remove, and change the items in the array.

We can create immutable arrays with let keyword when creating the array.

let a1 = ["D", "E", "F"]

Adding Items to Arrays

Arrays store items in a list that is indexed by integers starting with zero.

Use the += operator or the append function to add items to the end of an array.

a1+="Apples"
a1.append("Oranges")

a1 would now contain the two strings "Apples" and "Oranges".

To insert a new item to the middle of an array, use the insert function.

a1.insert("Swift", atIndex: 1)

Removing Items from Arrays

To remove items from arrays, use removeAtIndex().

Supply the index of the item to remove from the array.

The following code shows an example that you can use to remove items from arrays.

a1.removeAtIndex(0)
a1.removeLast()
a1.removeAll(keepCapacity: false)

The parameter in removeAll(keepCapacity:) lets you indicate whether you want the array to stay initialized for the number of items that the array contained.

If you know you are replacing the items immediately, it could save processing resources if you leave the array initialized.

Changing Items in Arrays

To change an item in an array, you simply reference the item index in square brackets and use the assignment operator to change the item.

var a1 = [1, 2, 0, 4, 5]
a1[2] = 3

Iterating Over Array Items

You can use the for in loop to do this.

var a1 = [1, 2, 3, 4, 5]
for i in a4{
    println("i = \(i)")
}

The code above generates the following result.

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