JuniorTheoryCommon

What does the program print?

SWIFT

enum Category: CaseIterable { case food, taxi }
struct Expense {
    let category: Category
    let cost: Double
}
let ride = Expense(category: .taxi, cost: 3.5)
let lunch = Expense(category: .food, cost: 2)
var totals: [Category: Double] = [:]
for e in [ride, lunch, ride] {
    totals[e.category, default: 0] += e.cost
}
print(Category.allCases.map { totals[$0, default: 0] })

[2.0, 7.0]

Expecting [7.0, 2.0]: thinking the totals keep the order in which the categories first appeared. map walks allCases, which lists food first, as declared.
Expecting a compile error: thinking an enum must be marked Hashable to be a dictionary key. Swift makes an enum without associated values Hashable by itself.

What does the program print if taxi is declared before food?
Why does totals.keys.sorted() not compile here, and how else can the totals be printed in a fixed order?

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JuniorTheoryCommon

What does the program print?

SWIFT

enum Category: CaseIterable { case food, taxi }
struct Expense {
    let category: Category
    let cost: Double
}
let ride = Expense(category: .taxi, cost: 3.5)
let lunch = Expense(category: .food, cost: 2)
var totals: [Category: Double] = [:]
for e in [ride, lunch, ride] {
    totals[e.category, default: 0] += e.cost
}
print(Category.allCases.map { totals[$0, default: 0] })

[2.0, 7.0]

Expecting [7.0, 2.0]: thinking the totals keep the order in which the categories first appeared. map walks allCases, which lists food first, as declared.
Expecting a compile error: thinking an enum must be marked Hashable to be a dictionary key. Swift makes an enum without associated values Hashable by itself.

What does the program print if taxi is declared before food?
Why does totals.keys.sorted() not compile here, and how else can the totals be printed in a fixed order?

Back to questions Open topic in roadmap →Answer it yourself — Quiz