Structures

Structures, are used to programmatically represent a real-life object in code. They are created with the struct keyword, followed by its name, and then body which contains its properties and methods.

struct Building {
  var address: String
  var floors: Int

  init(address: String, floors: Int, color: String) {
    self.address = address
    self.floors = floors
  }
}

Note: All stored properties of structures must conform to Hashable Protocol.

Default Property Values

A structure’s properties can have preassigned default values to avoid assigning values during initialization. Optionally, these properties’ values can still be assigned a value during initialization.

struct Car {
  var numOfWheels = 4
  var topSpeed = 80
}

var reliantRobin = Car(numOfWheels: 3)

print(reliantRobin.numOfWheels) // Prints: 3
print(reliantRobin.topSpeed)    // Prints: 80

Structure Instance Creation

A new instance of a structure is created by using the name of the structure with parentheses () and any necessary arguments.

struct structName {
  var propertyName: Type
  // Other properties go here
  // followed by any methods.
}

// Create an instance with properties passed in
var instanceName(propertyName: propertyValue, ...)

init() Method

Structures can have an init() method to initialize values to an instance’s properties. Unlike other methods, The init() method does not need the func keyword. In its body, the self keyword is used to reference the instance itself.

  init(propertyName: Type, ...) {
    self.propertyName = propertyName
    // Other instance properties go here.
  }

Structure Methods

Methods are like functions that are specifically called on an instance. To call the method, an instance is appended with the method name using dot . notation, followed by parentheses that include any necessary arguments.

struct Dog {
  func bark() {
    print("Woof")
  }
}

let fido = Dog()
fido.bark() // Prints: Woof

var newTV = TV(screenSize: 65, displayType: "LED")

// Instance of Person:
var morty = Person(name: "Morty", age: 14)

Mutating Methods

Structure methods declared with the mutating keyword allow the method to affect an instance’s own properties.

struct Menu {
  var menuItems = ["Fries", "Burgers"]

  mutating func addToMenu(dish: String) {
    self.menuItems.append(dish)
  }
}

var dinerMenu = Menu()

dinerMenu.addToMenu(dish: "Toast")

print(dinerMenu.menuItems)
// Output: ["Fries", "Burgers", "Toast"]