Dart Fundamentals

What is Dart?

Dart is the programming language Flutter uses, created by Google. It’s easy to pick up if you know any C-style language (Java, JavaScript, Swift, Kotlin). It’s modern, type-safe, and null-safe, and it compiles to fast native code for release builds.

Variables and types

var name = 'Anand';     // type inferred as String
String city = 'Delhi';  // explicit type
final pi = 3.14;        // set once, can't change
const max = 100;        // compile-time constant
int age = 25;
double price = 99.5;
bool isActive = true;

final and const both mean “can’t be reassigned”; the difference is const must be known at compile time. Prefer them over var when a value won’t change.

Null safety

Like Kotlin and Swift, Dart is null-safe: a variable can’t be null unless you add a ?. This stops a huge class of crashes.

String name = 'Anand';   // can never be null
String? nickname;        // may be null
print(nickname ?? 'Guest');   // ?? provides a default
print(nickname?.length);      // ?. safe access

Functions

int add(int a, int b) => a + b;          // arrow for one-liners

String greet(String name, {String greeting = 'Hi'}) {  // named param + default
  return '$greeting, $name!';
}

greet('Anand');                  // Hi, Anand!
greet('Priya', greeting: 'Hello');

The { } makes parameters named — Flutter uses these everywhere (you’ll see Text('hi', style: ...)), which makes widget constructors very readable.

Collections

final nums = [1, 2, 3, 4];                 // List
final ages = {'Anand': 28, 'Priya': 34};   // Map
final unique = {1, 1, 2};                  // Set -> {1, 2}

final doubled = nums.map((n) => n * 2).toList();   // [2,4,6,8]
final evens = nums.where((n) => n.isEven).toList(); // [2,4]
final total = nums.fold(0, (sum, n) => sum + n);    // 10

Classes

class User {
  final int id;
  final String name;
  User(this.id, this.name);          // shorthand constructor

  String describe() => 'User #$id: $name';
}

final u = User(1, 'Anand');
print(u.describe());

Async with Future and async/await

Future<String> loadData() async {
  await Future.delayed(Duration(seconds: 1));   // pretend network call
  return 'Done';
}

void main() async {
  final result = await loadData();   // waits without blocking
  print(result);
}

Common mistakes

• Using var everywhere instead of final/const for fixed values.
• Forgetting .toList() after map/where (they return lazy iterables).
• Calling an async function without await and wondering why the result is a Future.

Summary: Dart is a modern, null-safe language. Use final/const, handle nullables with ?/??, lean on named parameters (Flutter loves them), and use async/await with Future for asynchronous work.