Basics

Hello World

void main() {
  print('Hello, Dart!');
}

Variables

var name = 'Dart';       // type inferred
String lang = 'Dart';    // explicit type
final pi = 3.14;         // runtime constant
const max = 100;         // compile-time constant

String Interpolation

var name = 'World';
print('Hello, $name!');
print('1 + 1 = ${1 + 1}');

Types

Built-in Types

int	64-bit integer
double	64-bit floating point
num	Supertype of int and double
String	UTF-16 string
bool	true or false
List	Ordered collection (array)
Set	Unordered unique collection
Map	Key-value pairs
dynamic	Any type, disables static checking
void	No return value

Type Checks & Casts

if (obj is String) print(obj.length);
var s = obj as String;   // cast
print(obj.runtimeType);  // runtime type

Functions

Function Syntax

int add(int a, int b) => a + b;
void greet({required String name}) {
  print('Hello, $name');
}

Parameters

int f(int a)	Required positional parameter
int f([int a = 0])	Optional positional with default
f({required int a})	Required named parameter
f({int a = 0})	Optional named with default

Closures & Tearoffs

var square = (int n) => n * n;
[1, 2, 3].map((e) => e * 2);
[1, 2, 3].forEach(print);  // tearoff

Control Flow

Conditionals

if (x > 0) { print('pos'); }
else if (x == 0) { print('zero'); }
else { print('neg'); }
var result = x > 0 ? 'pos' : 'neg';

Loops

for (var i = 0; i < 5; i++) { }
for (var item in list) { }
while (x > 0) { x--; }
do { x--; } while (x > 0);

Switch & Pattern Matching

switch (color) {
  case 'red':   print('R'); break;
  case 'blue':  print('B'); break;
  default:      print('?');
}

Classes

Class Definition

class Point {
  final double x, y;
  Point(this.x, this.y);
  double distanceTo(Point p) =>
    sqrt(pow(x - p.x, 2) + pow(y - p.y, 2));
}

Named & Factory Constructors

class Point {
  double x, y;
  Point(this.x, this.y);
  Point.origin() : x = 0, y = 0;
  factory Point.fromJson(Map j) =>
    Point(j['x'], j['y']);
}

Inheritance

class Animal { void speak() {} }
class Dog extends Animal {
  @override
  void speak() => print('Woof');
}

Mixins & Extensions

Mixins

mixin Flyable {
  void fly() => print('Flying');
}
class Bird with Flyable {}

Extension Methods

extension StringX on String {
  String capitalize() =>
    '${this[0].toUpperCase()}${substring(1)}';
}
print('hello'.capitalize()); // Hello

Abstract & Implements

abstract class Shape {
  double area();
}
class Circle implements Shape {
  final double r;
  Circle(this.r);
  @override double area() => pi * r * r;
}

Async/Await

Futures

Future fetchData() async {
  var res = await http.get(uri);
  return res.body;
}

Streams

Stream count(int n) async* {
  for (var i = 0; i < n; i++) {
    yield i;
  }
}

Error Handling

try {
  var data = await fetchData();
} on HttpException catch (e) {
  print('HTTP error: $e');
} catch (e) {
  print('Error: $e');
}

Collections

List Operations

var nums = [1, 2, 3];
nums.add(4);
nums.where((n) => n > 2);     // [3, 4]
nums.map((n) => n * 2);        // [2,4,6,8]
var sorted = nums..sort();

Map Operations

var m = {'a': 1, 'b': 2};
m['c'] = 3;
m.containsKey('a');  // true
m.entries.map((e) => '${e.key}=${e.value}');

Spread & Collection If/For

var all = [0, ...nums];
var nav = ['Home', if (isAdmin) 'Admin'];
var sq = [for (var i in nums) i * i];

Null Safety

Nullable Types

int?	Nullable int (can be null)
int	Non-nullable int (never null)
!	Null assertion operator
?.	Null-aware access
??	Default if null
??=	Assign if null
late	Deferred initialization

Null Safety Examples

String? name;            // nullable
int len = name?.length ?? 0;
late final String title; // set before use
name ??= 'default';     // assign if null

Common Patterns

Enum with Values

enum Color {
  red('FF0000'), green('00FF00');
  final String hex;
  const Color(this.hex);
}

Records & Destructuring

(String, int) userInfo() => ('Alice', 30);
var (name, age) = userInfo();
print('$name is $age');

Sealed Classes

sealed class Shape {}
class Circle extends Shape { final double r; Circle(this.r); }
class Rect extends Shape { final double w, h; Rect(this.w, this.h); }

DART QUICK REFERENCE