Variables & Functions
var name = 'Ava'; // inferred
final age = 29; // set once
const pi = 3.14159; // compile-time constant
int square(int x) => x * x;
String greet(String name, {String greeting = 'Hi'}) => '$greeting, $name';
Null Safety
String? nickname; // nullable
String display = nickname ?? 'Guest';
nickname!.toUpperCase(); // force unwrap
a ??= 'default'; // assign if null
int? x;
x?.toString(); // safe call
Collections
List<String> list = ['a', 'b'];
Set<int> set = {1, 2, 3};
Map<String, int> map = {'a': 1};
list.map((e) => e.toUpperCase()).toList();
list.where((e) => e.length > 1);
list.fold(0, (sum, e) => sum + e.length);
Classes
class Point {
final double x, y;
Point(this.x, this.y);
Point.origin() : x = 0, y = 0;
}
class Dog extends Animal with Swimmer {
Dog(super.name);
@override
String speak() => '${super.speak()}, bark!';
}
mixin Swimmer { String swim() => 'swimming'; }
Async
Future<String> fetch() async {
await Future.delayed(Duration(seconds: 1));
return 'done';
}
try {
final result = await fetch();
} catch (e) { }
final results = await Future.wait([fetch(), fetch()]);
Stream<int> count() async* {
for (int i = 0; i < 3; i++) yield i;
}
Generics
class Box<T> {
final T value;
Box(this.value);
}
T firstOr<T>(List<T> items, T fallback) =>
items.isEmpty ? fallback : items.first;
class NumBox<T extends num> { } // bounded generic
Pattern Matching (Dart 3)
(String, int) record = ('Ava', 29);
final (name, age) = record; // destructuring
String describe(Object v) => switch (v) {
int n when n < 0 => 'negative',
int n => 'number: $n',
String s => 'string: $s',
_ => 'unknown',
};
