Posted on Jul 26, 2020

CS193p Notes - Lecture 4: Grid + enum + Optionals

Grid

init (_ items: [Item], viewForItem: @escaping (Item) -> ItemView) { self.items = items self.viewForItem = viewForItem }

@escaping is required because function is not used inside init but used somewhere else.

extension Array where Element: Identifiable { func firstIndex(matching: Element) -> Int { for index in 0..<self.count { if self[index].id == matching.id { return index } } return 0 } }

Adds new function to all Arrays where elements are identifiable
Name of the file Array+Identifiable tells that it's identifiable extension to Array

Enum

enum FastFoodMenuItem { case hamburger(numberOfPatties: Int) case fries(size: FryOrderSize) case drink(String, ounces: Int) case cookie } enum FryOrderSize { case large case small } let menuItem: FastFoodMenuItem = FastFoodMenuItem.hamburger(patties: 2)

Enums can contain extra data that's just for specific item like fries can be small or large.

Optional

enum Optional<T> { case none case some(T) }

An optional is an enum.

var hello: String? var hello: Optional<String> = .none var hello: String? = "hello" var hello: Optional<String> = .some("hello") var hello: String? = nil var hello: Optional<String> = .none

It's possible to get the value from optional two ways

hello! // this crashes the program in case the value is none if let safehello = hello { print(safehello) } else { // do something else }

Default

hello ?? "This is default value"

comma in if statement is like sequential && operator meaning that the value that is assigned in first condition can be used in the second condition.

var indexOfTheOneAndOnlyFaceUpCard: Int? { get { var faceUpCardIndices = [Int]() for index in cards.indices { if cards[index].isFaceUp { faceUpCardIndices.append(index) } } if faceUpCardIndices.count == 1 { return faceUpCardIndices.first } else { return nill } } set { for index in cards.indices { if index == newValue { cards[index].isFaceUp = true } else { cards[index].isFaceUp = false } } } }