README.md

Protocols

Slides

Agenda

• Recap on Protocols in Swift Standard Library
• Benefits using Protocols
• Extensions
• Pair-programming activity

Learning Objectives

By the end of this lesson, students should be able to:

• Work with extensions
• Use Protocols and Inheritance to build a character creation system
• Identify pros and limitations of protocols

Recap on Protocols activity from last class

let howManyTrees = Tree.allCases.count
//4

CaseIterable Protocol

let addresses = [StreetAddress("1490", "Grove Street"),
                 StreetAddress("2119", "Maple Avenue"),
                 StreetAddress("1400", "16th Street")]
let home = StreetAddress("1400", "16th Street")
print(addresses[0] == home)

Equatable Protocol

let ingredients: Set = ["cocoa beans", "sugar", "cocoa butter", "salt"]
if ingredients.contains("sugar") {
    print("No thanks, too sweet.")
}

Hashable Protocol

let bugs = ["Ant", "Spider", "Mantis", "Fly", "Caterpillar"]
for bug in bugs {
    print(bug)
}

Sequence Protocol

let text = "Hello, hello, hello again."
if let firstComma = text.firstIndex(of: ",") {
    print(text[..<firstComma])
}

Collection Protocol

Mini challenge

Given the Artist struct below, implement the Equatable protocol. You'll define what makes two instances equal.

// Used by Artist to determine style of Artist
enum Style: String {
    case impressionism
    case surrealism
    case cubism
    case popArt
}

struct Artist {
    let name: String
    let style: Style
    let yearBorn: Int
}

// Example instances of Artists, use for testing your equatable
let monet = Artist(name: "Monet", style: .impressionism, yearBorn: 1840)
let dali = Artist(name: "Salvador Dali", style: .surrealism, yearBorn: 1904)
let andy = Artist(name: "Andy Warhol", style: .popArt, yearBorn: 1928)

//This is what we want to achieve, being able to compare artists like:

monet == dali //returns true? false?

Benefits observed

What are some benefits you've seen so far about using protocols?

Behavior similar to multiple-inheritance

Adopted by classes, structs & enums

Value types = less risk

Extensions

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

• Add computed properties
• Define methods
• Provide new initializers
• Make an existing type conform to a protocol

Protocols can be extended to provide methods, initializers, and computed property implementations to conforming types.

This allows us to define behavior on protocols themselves, rather than in each type’s individual conformance.

extension FullName {
    func printUppercase(){
        print(fullName.uppercased())
    }
}

var me = Person(firstName: "Haruki", lastName: "Murakami")
me.printUppercase()

Providing default functionality

extension FullName {
    func printToConsole(){
        print(fullName)
    }
}

var me = Person(firstName: "Haruki", lastName: "Murakami")
me.printToConsole()

Food for thought

How to know when to use a subclass and an extension?

BREAK (10 min)

Checkpoint

What is a protocol in Swift?

What does it mean when a class conforms to a protocol?

Why is there a limitation when using OOP when it comes to inheritance?

How do protocols solve this limitation?

In Class Activity

In pairs, go over the following activity where you'll use inheritance and protocols to build the characters of a game.

RPG Game

Additional Resources

1. Sets
2. Hashable protocol
3. CaseIterable protocol
4. Sequence protocol
5. Collection protocol
6. Equatable protocol

1. POP usage with UIKit
2. Extensions
3. Article about protocols
4. Article on POP
5. More on Protocols
6. StackOverFlow answer