Swift Arrays

Arrays and dictionaries in Swift are objects that contain collections of other objects. In this lesson, we will cover some of the basics of working with arrays and dictionaries in Swift.

Mutable and immutable collections

Collections in Swift come in mutable and immutable forms. The contents of immutable collection instances cannot be changed after the object has been initialized. To make a collection immutable, assign it to a constant when it is created using the let keyword. On the other hand, collections are mutable if assigned to a variable (using var).

Swift array initialization

An array is a data type designed specifically to hold multiple values in a single ordered collection. An array, for example, could be created to store a list of String values. Strictly speaking, a single Swift-based array is only able to store values that are of the same type. An array declared as containing String values, therefore, could not also contain an Int value. However, it is also possible to create mixed type arrays. This will BE demonstrated later in this chapter. The type of an array can be specified using type annotation or left to the compiler to identify using type inference.

An array may be initialized with a collection of values (referred to as an array literal) at creation time using the following syntax:

var variableName: [type] = [value 1, value2, value3, ……. ]

The following code creates a new array assigned to a variable (thereby making it mutable) that is initialized with three string values:

var treeArray = ["Pine", "Oak", "Yew"]

Alternatively, the same array could have been created immutably by assigning it to a constant:

let treeArray = ["Pine", "Oak", "Yew"]

In the above instances, the Swift compiler will use type inference to ...