lazy & property observers
Use lazy stored properties for deferred work and observe changes on stored properties with willSet/didSet.
lazy & property observers is a free Swift Academy lesson on CoddyKit — lesson 2 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.
Overview
This lesson focuses on two essentials: lazy stored properties and property observers (willSet/didSet).
lazy property
lazy defers creation until first access. Useful for expensive work or when self is needed.
struct DataLoader {
lazy var data: [Int] = {
print("Loading data...")
return [1, 2, 3]
}()
}
var loader = DataLoader()
print("before access")
print(loader.data) // triggers initialization only nowlazy + self
Classes can use lazy to access self-dependent values after initialization.
class CacheOwner {
let name: String
lazy var hello: String = "Hi, " + name // uses self safely after init
init(name: String) { self.name = name }
}
let co = CacheOwner(name: "Ada")
print(co.hello)Property observers
Observers wrap changes around a stored property. Use newValue and oldValue for context.
struct Counter {
var value: Int = 0 {
willSet { print("will set to", newValue) }
didSet { print("did set from", oldValue) }
}
}
var c = Counter()
c.value = 5
c.value = 9Clamp with didSet
Use didSet to normalize or clamp values after assignment.
struct Score {
var raw: Int = 0 {
didSet {
if raw < 0 { raw = 0 }
if raw > 100 { raw = 100 }
}
}
}
var s = Score()
s.raw = 120 // clamped to 100
print(s.raw)
s.raw = -5 // clamped to 0
print(s.raw)Notes
Notes:
- lazy works only with var stored properties.
- Observers apply to stored properties; computed ones use get/set logic instead.
- Observers are not called during initialization before storage is ready.
lazy meaning
Quick check: What does lazy do?
Recap
Recap: Use lazy to delay heavy setup and willSet/didSet to react to stored property changes with simple rules.
Frequently asked questions
Is the “lazy & property observers” lesson free?
Yes — the full text of “lazy & property observers” 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 “lazy & property observers”?
Use lazy stored properties for deferred work and observe changes on stored properties with willSet/didSet. 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 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “lazy & property observers” 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