Arrays, Dictionaries & Sets
Create and use arrays, dictionaries, and sets. Iterate, update, and understand mutability.
Arrays, Dictionaries & Sets is a free Swift Academy lesson on CoddyKit — lesson 1 of 3. 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 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
Collections hold groups of values. Swift has Array, Dictionary, and Set.
Arrays
Array is an ordered list. Append with .append().
var numbers: [Int] = [1, 2, 3]
numbers.append(4)
print(numbers) // [1,2,3,4]Dictionaries
Dictionary stores key-value pairs. Keys must be unique.
var ages: [String:Int] = ["Ada":20, "Bob":25]
ages["Ada"] = 21
print(ages)Sets
Set stores unique values with no order.
var pets: Set<String> = ["dog", "cat"]
pets.insert("dog")
print(pets) // still only dog, catIteration
Use for-in to loop through arrays, dictionaries, or sets.
for n in numbers {
print(n)
}Mutability
Mutability: collections declared with let are fixed; with var they can change.
let fixed = [1,2,3] // constant array
// fixed.append(4) // error
var flexible = [1,2,3]
flexible.append(4) // worksSet question
Quick check: Which type stores unique unordered values?
Recap
Recap: Arrays are ordered lists, Dictionaries are key-value maps, Sets are unique unordered collections. Use var for mutable collections.
Frequently asked questions
Is the “Arrays, Dictionaries & Sets” lesson free?
Yes — the full text of “Arrays, Dictionaries & Sets” is free to read here on the web, and the Swift Academy course includes 3 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 “Arrays, Dictionaries & Sets”?
Create and use arrays, dictionaries, and sets. Iterate, update, and understand mutability. 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 3, so you can start here or from the beginning and move at your own pace.
How long does the “Arrays, Dictionaries & Sets” 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
- Arrays, Dictionaries & Sets
- Sets — membership & operations
- Iteration patterns & mutability