Swift Academy · Lesson

Arrays, Dictionaries & Sets

Create and use arrays, dictionaries, and sets. Iterate, update, and understand mutability.

Lesson 1 of 38 steps

Arrays, Dictionaries & Sets 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

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, cat

Iteration

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)  // works

Set question

Quick check: Which type stores unique unordered values?

Answer it in the interactive lesson

Recap

Recap: Arrays are ordered lists, Dictionaries are key-value maps, Sets are unique unordered collections. Use var for mutable collections.

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Frequently Asked Questions

Is the “Arrays, Dictionaries & Sets” lesson free?

Yes — any 3 lessons of the Swift Academy learning path, including “Arrays, Dictionaries & Sets”, 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 “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, 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 “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.

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