Define a basic struct with initialized properties and optional properties

struct Pixel {
    var positionX = 0
    var positionY = 0
    var height: Int? 
    var color: UIColor?
}

Define a basic struct with initialized properties

struct Pixel {
  var positionX = 0
  var positionY = 0
}

Create an instance with the standard values.

struct Pixel {
 var positionX = 0
 var positionY = 0
}
var myPixel = Pixel()

Access to properties

myPixel.positionX
myPixel.height

Set a value for a property

myPixel.height = 4
myPixel.color = UIColor.black

Create an instance of struct with the standard initializer.

struct Pixel {
 var positionX: Int
 var positionY: Int
}
let myPixel = Pixel(positionX: 4, positionY: 2)

struct are ... type

struct are value type

Computed properties for a struct

struct Pixel {
    var positionX : Int
    var positionY : Int
    var distanceToCenter : Double {
        return sqrt(Double(positionX^2 + positionY^2))
    }
}
let myPixel = Pixel(positionX: 7, positionY: 4)
print(myPixel.distanceToCenter)

Instance method modifying an instance property

struct Pixel {
    var positionX = 0
    var positionY = 0
    mutating func moveOneRight() {
        positionX += 1
    }
}
var pixel = Pixel()
pixel.moveOneRight()
    

Create a simple class with initializer

class Point {
    var posX: Float
    var posY: Float
    var color: UIColor?
    init (x: Float, y: Float) {
        self.posX = x
        self.posY = y
    }
}

Inheritance. Create a subclass

class SomeSubclass: SomeSuperclass {
 // properties and methods here
}

Subclassing. Overriding methods.

A subclass can modify an inherited property or method.

The new definition must have the prefix override.

Inheritance. How to access the superclass methods and properties from the subclass definition?

With the super prefix. 

super.someMethod()
super.someProperty

What are extensions?

Extensions add new functionality to an existing class, structure, enumeration, or protocol type.

This includes types to which one does not have access. (ex: Int, String).

Extension to test if a String contains the letter "a".

extension String {    
  var containsA: Bool {        
    return self.range(of: "a") != nil    
  }
}

Extension to add a given Int to an Int.

extension Int {
    func plusX(x: Int)->Int {
        return self + x
    }
}
2.plus(x: 3) //is 5

An extension can modify the value of the variable.

Example of an extension to add 1 to an Int.

extension Int {
    mutating func plus1() {
        self += 1
    }
}
let number = 2
number.plus1()
number // is 3