Properties & Subscripts
Use lazy stored properties, get/set computed properties, property observers, and subscripts for custom indexing.
Properties & Subscripts is a free Swift Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
This lesson covers advanced properties: lazy, computed with get/set, observers, plus custom subscripts.
lazy property
lazy properties are created only on first access. Useful for expensive work.
struct DataLoader {
lazy var data: [Int] = {
print("Loading...")
return [1,2,3]
}()
}
var loader = DataLoader()
print("before access")
print(loader.data)Computed get/set
Computed properties use get/set blocks to calculate or update values.
struct Circle {
var radius: Double
var diameter: Double {
get { return radius * 2 }
set { radius = newValue / 2 }
}
}
var c = Circle(radius: 5)
print(c.diameter) // 10
c.diameter = 20
print(c.radius) // 10Observers
Use willSet and didSet to react to property changes.
class Account {
var balance: Double = 0 {
willSet { print("Will set to", newValue) }
didSet { print("Did set from", oldValue) }
}
}
var a = Account()
a.balance = 50Subscript
Subscripts let you define custom access with bracket syntax.
struct TimesTable {
let multiplier: Int
subscript(i: Int) -> Int {
return multiplier * i
}
}
let three = TimesTable(multiplier: 3)
print(three[4]) // 12Multi-parameter subscript
Subscripts can take multiple parameters, e.g., a matrix with row and column indices.
struct Matrix {
var grid: [[Int]]
subscript(row: Int, col: Int) -> Int {
return grid[row][col]
}
}
let m = Matrix(grid:[[1,2],[3,4]])
print(m[1,0]) // 3lazy Q
Quick check: What does the lazy keyword do?
Recap
Recap: Use lazy for deferred init, get/set for computed props, willSet/didSet for observing, and subscripts for custom access.
Frequently asked questions
Is the “Properties & Subscripts” lesson free?
Yes — the full text of “Properties & Subscripts” is free to read here on the web, and the Swift Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Swift Academy course, upgrade to CoddyKit PRO.
What will I learn in “Properties & Subscripts”?
Use lazy stored properties, get/set computed properties, property observers, and subscripts for custom indexing. You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Swift Academy?
No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Properties & Subscripts” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Swift Academy lesson?
Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Properties & Subscripts
- lazy & property observers
- Computed properties with get/set
- Subscripts for custom indexing