Memberwise init & mutating methods
Understand Swift structs: auto-generated memberwise initializers and the need for mutating methods when changing properties.
Memberwise init & mutating methods is a free Swift Academy lesson on CoddyKit. This is lesson 1 of 3. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, and your progress syncs across the web and the CoddyKit app. The Swift Academy course includes 3 lessons in total.
Intro
Structs in Swift get a free memberwise initializer and require mutating for methods that modify state.
Memberwise init
Swift automatically provides an init(x:y:) for structs with stored properties.
struct Point {
var x: Int
var y: Int
}
let p = Point(x: 3, y: 5)
print(p.x, p.y)Non-mutating method
Methods without mutating cannot change properties—they are read-only by default.
struct Counter {
var count = 0
func show() { print(count) }
}
let c = Counter()
c.show()Mutating increment
Adding mutating lets a struct method modify its properties.
struct Counter {
var count = 0
mutating func increment() {
count += 1
}
}
var c = Counter()
c.increment()
print(c.count)Reassigning self
A mutating method can even reassign self entirely.
struct Switch {
var on: Bool = false
mutating func toggle() {
self = Switch(on: !on)
}
}
var s = Switch()
s.toggle()
print(s.on)Tips
Tips:
- Use mutating only when you must change properties.
- Keep most methods non-mutating for clarity.
- Remember classes do not need this keyword.
Mutating keyword
Quick check: Why does a struct method need mutating to modify properties?
Recap
Recap: Structs get a free memberwise initializer. Use mutating when a method changes state or reassigns self.
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Frequently Asked Questions
Is the “Memberwise init & mutating methods” lesson free?
Yes — any 3 lessons of the Swift Academy learning path, including “Memberwise init & mutating methods”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Swift Academy course includes 3 lessons in total.
What will I learn in “Memberwise init & mutating methods”?
Understand Swift structs: auto-generated memberwise initializers and the need for mutating methods when changing properties. 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, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 3.
How long does the “Memberwise init & mutating methods” 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
- Memberwise init & mutating methods
- Inheritance, overriding & final
- Access control (public/internal/fileprivate/private)