Intro to iOS Development
  • Welcome
    • β˜€οΈIntroduction
    • 🐣Getting Started
    • 🐦Course Staff
  • Logistics
    • πŸ“œSyllabus
    • πŸ—“οΈSchedule
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    • Ed Discussion
  • Assignments
    • 🍼A1: Swift Basics
    • πŸ§‘A2: Profile
    • πŸ’¬A3: ChatDev
    • πŸ‘¨β€πŸ³A4: ChefOS
    • πŸ‘¨β€πŸ³A4: ChefOS - SwiftUI
    • πŸ“±Hack Challenge
      • πŸ†FA23 Winners
  • Lectures
    • 1️⃣Logistics + Swift Basics
    • 2️⃣UIKit + AutoLayout
  • 3️⃣MVC + Navigation + Delegation
  • 4️⃣UITableView
  • 5️⃣UICollectionView
  • 6️⃣Networking I
  • 7️⃣Networking II
  • 8️⃣SwiftUI I
  • 9️⃣SwiftUI II
  • πŸ”ŸPersistence + SnapKit
  • πŸ””(11) Notifications
  • 🌎(12) Deployment and MapKit
  • Chapters
    • πŸ–οΈIntroduction
    • ☁️Git + GitHub
      • 1️⃣Git Installation
      • 2️⃣Git Basics
      • βž•Git+
    • 🐣Swift Basics
      • 1️⃣Variables and Constants
      • 2️⃣Data Types
      • 3️⃣Operators
      • 4️⃣Data Structures
      • 5️⃣Conditionals
      • 6️⃣Loops
      • 7️⃣Functions
      • 8️⃣Closures
      • 9️⃣Optionals
    • 🧰UIKit + AutoLayout
      • 1️⃣Classes
      • 2️⃣UIKit
      • 3️⃣AutoLayout
    • πŸ“ΊMVC + Navigation + Delegation
      • 1️⃣MVC
      • 2️⃣Navigation
      • 3️⃣Delegation
    • πŸ“UITableView
      • 1️⃣What is a UITableView?
      • 2️⃣UITableView Setup
    • πŸ“šUICollectionView
      • 1️⃣What is a UICollectionView?
      • 2️⃣UICollectionView Setup
    • 🌐Networking I
      • 1️⃣HTTP Requests
      • 2️⃣Callbacks
      • 3️⃣Codable
    • 🌍Networking II
      • 1️⃣Alamofire
      • 2️⃣GET Requests
      • 3️⃣POST Requests
      • 4️⃣URLSession
    • πŸ’ΎPersistence + SnapKit
      • 1️⃣Persistence
      • 2️⃣SnapKit
    • πŸ•ŠοΈSwiftUI
      • 1️⃣Introduction to SwiftUI
      • 2️⃣Getting Started with SwiftUI
      • 3️⃣Views + Modifiers
      • 4️⃣Layouts
      • 5️⃣Navigation
      • 6️⃣Property Wrappers
    • πŸŽ›οΈWidgets
      • 1️⃣Introduction to Widgets
      • 2️⃣Setting Up Widgets
      • 3️⃣Building Widgets
      • 4️⃣Configuring Widgets
    • 🧱Project Foundation
    • βœ…Testing
      • 1️⃣Unit Testing
    • πŸ‘£Debugging
      • 1️⃣OSLog
      • 2️⃣Crashlytics
      • 3️⃣Analytics
    • ☁️CI/CD
      • 1️⃣Xcode Cloud
      • 2️⃣AppStore Shipping
  • Guides
    • πŸ”¨Xcode Project Setup
    • 🎨Figma
    • πŸ“¬Postman
    • πŸ₯₯CocoaPods
    • 🧰UIKit Handbook
    • πŸ“‘Tab Views
      • UITabBarController
      • TabView
  • Work in progress
    • 🧡Concurrency
    • 2️⃣UI Testing
    • πŸ•Reactive Programming
    • 🧠Memory Management
      • πŸ”ARC
    • πŸ“¦Storage
    • πŸ“£Notifications
  • Archived
    • SP24
      • Logistics
        • πŸ“œSyllabus
        • πŸ—“οΈSchedule
        • πŸ–ŠοΈGrading
        • πŸ™‹β€β™‚οΈOffice Hours
      • Assignments
        • 🍼A1: Swift Basics
        • πŸ§‘A2: Profile
        • πŸ’¬A3: ChatDev
        • πŸ‘¨β€πŸ³A4: ChefOS
        • πŸ“±Hack Challenge
          • πŸ†FA23 Winners
      • Lecture
        • 0️⃣Course Intro + Logistics + Git Setup
        • 1️⃣Swift Basics
        • 2️⃣UIKit + AutoLayout
        • 3️⃣MVC + Navigation + Delegation
        • 4️⃣UITableView
        • 5️⃣UICollectionView
        • 6️⃣Networking I
        • 7️⃣Networking II
        • 8️⃣Persistence + SnapKit
        • πŸ”ŸSwiftUI
        • πŸ”’TabViews
    • FA23
      • Logistics
        • 🐣Getting Started
        • 🐦Course Staff
        • πŸ“œSyllabus
        • πŸ—“οΈSchedule
        • πŸ–ŠοΈGrading
        • πŸ™‹β€β™‚οΈOffice Hours
      • Assignments
        • 🍼A1: Swift Basics
        • πŸ§‘A2: Profile
        • πŸ’¬A3: ChatDev
        • πŸ‘¨β€πŸ³A4: ChefOS
        • πŸ“±Hack Challenge
          • πŸ†FA23 Winners
      • Lectures
        • 0️⃣Course Intro + Logistics
        • 1️⃣Swift Basics
        • 2️⃣UIKit + AutoLayout
        • 3️⃣MVC + Navigation + Delegation
        • 4️⃣UITableView
        • 5️⃣UICollectionView
        • 6️⃣Networking I
        • 7️⃣Networking II
        • 8️⃣Persistence + SnapKit
        • πŸŽ›οΈWidgets
          • πŸ‘ΌIntroduction to Widgets
          • βš’οΈSetting Up Widgets
          • 🧱Building Widgets
          • πŸ‘¨β€πŸ’»Configuring Widgets
        • πŸ”ŸSwiftUI
    • SP23
      • Logistics
        • Lecture Schedule
        • Syllabus
        • Grading
        • SP23 Office Hours
      • Chapters
        • 1. Intro to Swift & Xcode
          • Lecture Handout
          • Lecture Demo
          • 🍼Project: Swift Basics
        • 2. UIKit and AutoLayout
          • Lecture Handout
          • Lecture Demo
          • πŸ›’Project: UIKit + AutoLayout
        • 3. Navigation, MVC, and Delegation
          • Lecture Handout
          • Lecture Demo
          • Project: Navigation + Delegation
        • 4. UITableView
          • Lecture Handout
          • Lecture Demo
          • Project: UITableView
        • 5. UICollectionView
          • Lecture Handout
          • Lecture Demo
          • Project: UICollectionView
        • 6. Networking I
          • Lecture Handout
          • Lecture Demo
          • Project: Persistence
        • 7. Networking II
          • Lecture Handout
          • Lecture Demo
            • Message Board
          • Project: Networking II
        • 8. Swift UI
        • 9. CocoaPods
          • 🍫Lecture Handout
          • πŸ§‘β€πŸ³Lecture Demo
      • Cheat Sheets
        • Setting Up a New Xcode Project
        • Submitting Your Projects
        • Setting Up CocoaPods
    • 2022
      • SwiftUI
    • 2021
      • Adding Flare
      • Project: UIView Animations (Optional - Extra Credit)
      • UIView Animations
      • Xcode Tips and Tricks
    • 2019
      • Firebase
      • Persistence: UserDefaults
  • Swift Guide (ARCHIVED)
    • About this Textbook
    • Documentation
    • Constants and Variables
      • Variable Properties
      • Lazy and Static Variables
    • Functions
    • Ranges
    • Arrays
      • Basic Array Operations
      • Iteration and Enumeration
      • Advanced Array Operations
    • Tuples
    • Conditions and While Loops
    • For Loops
    • Enums and Switches
      • Enums with Associated Values
      • Indirect Enums
    • Classes and Structs
    • Optionals
    • Dictionaries
      • Dictionary Implementation
    • Closures
    • Constraints
    • Generics
    • Protocols
      • Protocols With Associated Types
    • Casting
    • Errors
    • Networking
      • Result
    • Inout
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  • Type Constraints
  • Switch Constraints

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  1. Swift Guide (ARCHIVED)

Constraints

For those of you looking for help on autolayout, this is not the place. Constraints, the constraints defined in Swift Standard Library, are an advanced topic that builds on other advanced topics, so beware.

Everything in this article center around the where keyword. The where keyword allows us to make new components conditional or add extra conditions onto switches!

Type Constraints

When working with parametric polymorphism it makes sense to add functionality in certain cases.

For the following examples, we will use this implementation of a binary tree:

enum BinaryTree<T> {
    case leaf
    indirect case node(left: BinaryTree, value: T, right: BinaryTree)
}

Let's say we want to add a function to tell if our binary tree contains a value. To do this, we need == to be implemented. Thus, we make a function that will exist if and only if T conforms to Equatable:

extension BinaryTree where T: Equatable {
    
    func contains(_ element: T) -> Bool {
        switch self {
            case .leaf: return false
            case let .node(left, value, right):
                if value == element {
                    return true
                }
                return left.contains(element) || right.contains(element)
        }
    }
    
}

For those of you acquainted with binary trees, you may look at this and want to throw up–sorry! This is quite inefficient. The point of a binary tree is that we can reduce runtime by organizing it. And to be fair, that fact kind of nullifies this whole conditional function business, but we can think of this as more of an exercise than an actual use case.

But, I digress. Let's fix our inefficiency. There is another protocol we can use Comparable. Comparable guarantees ==, <, and >. With these, it also guarantees <= and >=. Perfect! Let's implement it.

extension BinaryTree where T: Comparable {
    func contains(_ element: T) -> Bool {
        switch self {
            case .leaf: return false
            case let .node(left, value, right):
                if value == element {
                    return true
                } else if element < value {
                    return left.contains(element)
                } else {
                    return right.contains(element)
                }
        }
    }
}

You may not like having two extensions because it just gets kind of messy, but do not fear, we can combine these by putting the constraints on the functions instead of the extensions:

extension BinaryTree {

    func contains(_ element: T) -> Bool where T: Equatable {
        switch self {
            case .leaf: return false
            case let .node(left, value, right):
                if value == element {
                    return true
                }
                return left.contains(element) || right.contains(element)
        }
    }
    
    func contains(_ element: T) -> Bool where T: Comparable {
        switch self {
            case .leaf: return false
            case let .node(left, value, right):
                if value == element {
                    return true
                } else if element < value {
                    return left.contains(element)
                } else {
                    return right.contains(element)
                }
        }
    }

}

Switch Constraints

Some of you may still be grossed out. I promised you that switch statements were this wonderful feature that would figure out all of the cases necessary to process something, but here I need extra if statements 😀! And you'd be right, except for that last part... We can cover these cases as well.

We can add conditionality to our cases with the where keyword.

func contains(_ element: T) -> Bool {
    switch self {
        case .leaf: return false
        case let .node(_, value, _) where value == element: return true
        case let .node(left, value, _) where value < element: return left.contains(element)
        case let .node(_, _, right): return right.contains(element)
    }
}

Note that since the last case will always be triggered for nodes, it must be last. I wanted to add a where clause to fix that, but Swift would not recognize that as covering all of the cases. This was the cleanest solution we found. Credits to Hanzheng Li '23 for fixing that one.

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Last updated 3 years ago

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