LearnLists: Fixed-Length, Growable & Index Operations

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Lesson 19 of 59

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Lists: Fixed-Length, Growable & Index Operations

In Plain English

A `List<T>` (array equivalent) is an ordered collection of elements. Lists in Dart can be growable (default `[...]` literals that expand dynamically with `.add()`) or fixed-length (`List.filled(5, 0, growable: false)` for cache-efficient pre-allocated memory buffers). Lists are 0-indexed and provide methods like `.contains()`, `.indexOf()`, `.sublist()`, and `.sort()`.

The Mental Model

"A growable list is like a loose-leaf binder where you can insert new pages anytime; a fixed-length list is a hardbound notebook with exactly 100 numbered pages."

Deep Dive: How It Works

Growable vs Fixed: Growable lists dynamically resize memory arrays; fixed-length lists disallow `.add()` or `.remove()`.

Index Access: `list[0]` for read, `list[1] = value` for write.

Immutable Lists: `List.unmodifiable([1, 2, 3])` prevents all subsequent mutations at runtime.

Syntax Blueprint

var fruits = ["Apple", "Banana"]; // Growable List<String>
fruits.add("Cherry");
fruits.remove("Banana");
print(fruits[0]); // "Apple"

Growable list declaration, mutation, and index access.

Core Rules to Remember

0-Indexed Ordered Sequences: Elements maintain strict insertion order and can contain duplicates.

Growable by Default: List literals automatically expand as elements are appended.

Unmodifiable Protection: Wrap sensitive state in `List.unmodifiable()` to prevent accidental mutations.

Common Beginner Traps & How to Fix Them

Mistake:Accessing `list[list.length]` and encountering `RangeError (index)`.

Why it happens: Lists are 0-indexed; the final element is at index `list.length - 1` (or use `list.last`).

How to fix: Use `list.first` and `list.last` for safe boundary element access.

Pro Tip: Use `List.generate(10, (i) => i * 2)` for clean, programmatic list instantiation.

Live Interactive Example

Hit Run Code to see it live

List Manipulation and Indexing

Python 3.12

Output Console

Click "Run Code" to view the rendered output.

How it works: Appended an element, sorted in-place, and sliced top scoring sublist.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Initialize and Sift List

Create a growable list `final list = [3, 1, 4];`.
Add `2` using `.add(2)`, sort the list with `.sort()`.
Print `List: $list`.

Sandbox Output

Click "Run & Check" to test your solution.

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