Generic Collections in Practice
Type List, Map, and custom containers.
Generic Collections in Practice is a free Dart Academy lesson on CoddyKit — lesson 4 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.
Collections Are Generic
Dart's everyday collections are all generic. List, Set, and Map each take type parameters that lock in what they hold. 📦
Typing a List
A List takes one type parameter for its elements. Declaring List of String means every item must be a String.
List<String> names = ['Ada', 'Linus'];Typing a Set
A Set works the same way and keeps elements unique. Set of int holds whole numbers with no duplicates.
Set<int> ids = {1, 2, 2, 3};Typing a Map
A Map takes two type parameters: one for keys and one for values. Order matters, with the key type listed first.
Map<String, int> ages = {'Ada': 36};Inference From Literals
When you write a literal, Dart often infers the type from its contents. A list of numbers becomes List of int automatically.
var scores = [90, 85, 100];Annotate Empty Literals
An empty literal has nothing to infer from, so add the type yourself. Otherwise Dart may guess a type you did not want.
var queue = <String>[];Element Types Flow Through
Once typed, methods return the right element type. Reading from a List of String gives a String, ready to use directly.
List<String> names = ['Ada'];
String first = names.first;Nesting Generics
Type parameters can nest as deep as you need. A Map from String to List of int is perfectly valid and fully checked.
Map<String, List<int>> grades = {
'Ada': [90, 85]
};Generics Meet Transforms
Methods like map carry types through a pipeline. Mapping ints to their strings yields an Iterable of String.
var labels = [1, 2].map((n) => 'n=$n');Custom Generic Containers
Your own generic classes plug into this world too. A Stack of T can store whatever element type the caller chooses.
class Stack<T> {
final _items = <T>[];
void push(T x) => _items.add(x);
}Safety End to End
From declaration to transform to storage, the type stays known. That is the payoff: reuse and full checking, all the way through.
Quick Check
How many type parameters does a Map take?
Recap
You typed List, Set, and Map, relied on inference, annotated empty literals, and nested generics. Types flow safely through every transform. ✅
Frequently asked questions
Is the “Generic Collections in Practice” lesson free?
Yes — the full text of “Generic Collections in Practice” 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 “Generic Collections in Practice”?
Type List, Map, and custom containers. 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 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Generic Collections in Practice” 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
- Why Generics Beat dynamic
- Generic Classes and Methods
- Bounded Type Parameters With extends
- Generic Collections in Practice