Dart Cheatsheet - Dart Syntax & Flutter Reference

This reference is for Dart developers building Flutter apps or backend services, centered on the syntax you write all day: null-safe variables (final/const vs late), functions and closures, classes with mixins, and async flow with Future/async/await. Unlike a flat Dart feature list, entries are grouped by the construct and flag null-safety behavior that trips people new from Java/JS. After reading you should be able to write null-safe chains without non-null assertions everywhere, compose classes with mixins, and handle asynchronous work with Future and async/await without blocking the UI thread.

Languages·43 commands·Last updated 2026-07-21

Variables & Types 10

var name = 'Dart';

Type inference

String name = 'Dart';

Explicit type

final name = 'Dart';

Final variable (runtime constant)

const pi = 3.14;

Compile-time constant

int? nullableInt;

Nullable type

late String lateVar;

Late initialization

dynamic anything = 42;

Dynamic type

List<int> numbers = [1, 2, 3];

List

Map<String, int> ages = {'Alice': 25};

Map

Set<int> unique = {1, 2, 3};

Set

Functions & Closures 6

int add(int a, int b) => a + b;

Arrow function

void greet(String name, [String? title]) { }

Optional positional parameter

void greet({required String name, int age = 0}) { }

Named parameters

Function fn = (x) => x * 2;

Closure

void Function(int) callback;

Function type

typedef Comparator<T> = int Function(T a, T b);

Type alias

Classes & Mixins 7

class Person { String name; Person(this.name); }

Class and constructor

class Student extends Person { }

Inheritance

class Flyable mixin Fly { }

mixin

class Bird extends Animal with Flyable { }

Use a mixin

abstract class Shape { double area(); }

Abstract class

class Singleton { static final instance = Singleton._(); Singleton._(); }

Singleton pattern

class Immutable { final int value; const Immutable(this.value); }

Immutable class

Null Safety 6

String? nullable;

Nullable declaration

nullable?.length

Safe call

nullable ?? 'default'

Null-coalescing operator

nullable!

Non-null assertion

if (nullable != null) { nullable.length; }

Type promotion

late String lateVar;

Late initialization (must be assigned before use)

Asynchronous 6

Future<int> fetchData() async { return 42; }

Async function

int result = await fetchData();

Await an async result

Stream<int> countStream() async* { yield 1; }

Async generator

await for (var value in stream) { }

Listen to a stream

Future.wait([future1, future2]);

Await multiple futures

Completer<int> completer = Completer();

Manually control a Future

Collection Operations 8

list.where((x) => x > 5).toList()

Filter

list.map((x) => x * 2).toList()

Map

list.reduce((a, b) => a + b)

Reduce

list.fold(0, (sum, x) => sum + x)

Fold

list.any((x) => x > 0)

Any exists

list.every((x) => x > 0)

All satisfy

list.sort((a, b) => a.compareTo(b))

Sort

list.groupBy((x) => x.category)

Group (needs the collection package)

Tips

Dart's null safety is a compile-time check; use ? and ?? to avoid runtime exceptions.
async/await is core to asynchronous programming; avoid blocking the UI thread.
mixin is Dart's way to achieve multiple inheritance; good for code reuse.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Official Docs

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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