Sets and Guaranteed Uniqueness
Store items without duplicates.
Sets and Guaranteed Uniqueness is a free Dart 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 Dart Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What a Set Is
A Set is an unordered collection where every item is unique. It is your go-to tool when duplicates simply should not exist. 👍
Creating a Set
Use curly braces with values to make a Set. Dart sees the items and knows this is a set, not a map.
var colors = {'red', 'green', 'blue'};Empty Sets Need a Type
Empty curly braces mean an empty map, not a set. To get an empty Set, write the type so Dart knows your intent.
var tags = <String>{};Duplicates Just Vanish
Adding a value that already exists changes nothing. A Set silently keeps only one copy of each item.
var nums = {1, 2, 2, 3};Adding Items
Call add to insert a value. If it is already present, the set stays the same and no error is thrown.
var s = <int>{};
s.add(5);
s.add(5);Removing Items
Use remove to take a value out. It returns true if the item was there and false if it was not.
var s = {1, 2, 3};
s.remove(2);Checking Membership
The contains method answers a yes-or-no question fast. This quick lookup is the real superpower of sets.
var s = {'a', 'b'};
print(s.contains('a'));How Big Is It
The length property tells you how many unique items live in the set right now.
var s = {1, 1, 2, 3};
print(s.length);Sets Are Unordered
Do not rely on the order of items in a Set. If you need a stable order, reach for a List instead.
From List to Set
Wrap a list in a set to drop duplicates instantly. This is the cleanest way to deduplicate values.
var unique = {1, 2, 2, 3}.toList();Looping a Set
A Set is iterable, so a for-in loop visits every unique item one by one.
for (var c in {'red', 'blue'}) {
print(c);
}Quick Check
You add the same value to a Set twice. What happens?
Recap
Nice work! A Set holds unique, unordered items with fast add, remove, and contains. Reach for it whenever duplicates do not belong. 🎉
Frequently asked questions
Is the “Sets and Guaranteed Uniqueness” lesson free?
Yes — the full text of “Sets and Guaranteed Uniqueness” is free to read here on the web, and the Dart 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 Dart Academy course, upgrade to CoddyKit PRO.
What will I learn in “Sets and Guaranteed Uniqueness”?
Store items without duplicates. You practise Dart 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 Dart Academy?
No prior experience is required. Dart 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 “Sets and Guaranteed Uniqueness” 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 Dart Academy lesson?
Yes. Every Dart 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
- Sets and Guaranteed Uniqueness
- Set Operations: union, intersection, difference
- Maps as Key-Value Stores
- Iterating Entries, Keys, and Values