Swift 5 - Object Oriented

copy-on-write optimization

copy-on-write optimization happens when one of its copies are modified. The copy that is being modified replaces its storage with a unique copy of itself, which is modified in place. The one that is modified incurs the cost of copying.

class Numbers {
    var value = 0
}

var originalArray = [Numbers(), Numbers()]
var copiedArray = originalArray

originalArray[0].value = 1
//: Updated value is reflected in both arrays because the line above only modifies the `value` of the object, `Numbers`
// originalArray = [1,0]
// copiedArray = [1,0]

originalArray[0] = Numbers()
//: Updated value is NOT reflected in both arrays because the line above modifies the entire object, `Numbers`. Now it references a different object for index 0
// originalArray = [0,0] 
// copiedArray = [1,0]

inheritance

In Swift, a class can only inherit from one parent class

class Shape {
    var height: Double = 0
    var width: Double = 0

    init(height: Double, width: Double) {
        self.height = height
        self.width = width
    }

    public func calculateArea() -> Double {
        return height * width
    }
}

//: Triangle inherits from Shape
class Triangle: Shape {
    var base: Double = 0

    init(height: Double, width: Double, base: Double) {
        //: Calls the parent class, Shape's init
        super.init(height: height, width: width)
        self.base = base
    }

    // overrides the parent class' function since it has a different implementation
    override public func calculateArea() -> Double {
        return (height * base) / 2
    }
}

var triangle = Triangle(height: 1.0, width: 2.0, base: 4)
print(triangle.calculateArea())

polymorphism

an object that can take on many forms

//: Triangle is of type Shape (the parent class) but it's also of type Triangle
var triangle: Shape
triangle = Triangle(height: 1.0, width: 2.0, base: 4)

print(triangle.calculateArea())

protocols

a protocol is similar to a contract. Any class that adheres to the protocol must implement every method on the protocol’s list
a protocol is a type and can be treated as such.

protocol Business {
    func sell() -> String
    func stockInventory() -> Bool
}

extensions

an extension enables you to add functionality to a class without ever modifying the original class definition.

extension GroceryStore: Business {
    func orderOnline() -> String {
        //...
    }
}

pass by value vs pass by reference

pass by value

an instance of a struct or a parameter
does not share or reference the same memory address for that instance
changing a property on the instance will only apply to the copy, and the original instance will remain unchanged.

pass by reference

an instance of a class
shares or references the same memory address for that instance
changing a value on a copy will also modify the original instance, since the copy is referencing the original.

swift 5 - object oriented

Swift 5 - Object Oriented

copy-on-write optimization

inheritance

polymorphism

protocols

extensions

pass by value vs pass by reference

pass by value

pass by reference