Dart Keywords

🔑 What are Dart Keywords?

Dart keywords are reserved words with special meanings in the language. They cannot be used as identifiers and control program flow, define types, and structure code.


// Keywords in action
class MyClass {
  final String name;
  static const int version = 1;
  
  MyClass(this.name);
}

Keywords used:

class - defines a class

final - creates immutable variable

static - class-level member

const - compile-time constant

Keyword Categories

🏗️

Declaration

Define variables and functions

var name = 'John';
final age = 25;
const pi = 3.14;

🔄

Control Flow

Control program execution

if (age > 18) {
  return 'Adult';
} else {
  return 'Minor';
}

🎯

Object-Oriented

Define classes and inheritance

class Animal extends Object {
  void speak() => print('Sound');
}

⚡

Async

Handle asynchronous operations

Future fetchData() async {
  await Future.delayed(Duration(seconds: 1));
  return 'Data loaded';
}

🔹 Variable Declaration Keywords

Keywords for declaring variables with different properties:

// var - type inferred
var message = 'Hello World';

// final - runtime constant (immutable)
final DateTime now = DateTime.now();

// const - compile-time constant
const String appName = 'My App';

// late - lazy initialization
late String expensiveValue;

Usage:

var: Type determined automatically

final: Set once, cannot change

const: Known at compile time

late: Initialize when first used

🔹 Control Flow Keywords

Keywords that control how your program executes:

🔸 Conditional Keywords

// if, else, else if
int score = 85;
if (score >= 90) {
  print('A grade');
} else if (score >= 80) {
  print('B grade');
} else {
  print('Try harder');
}

// switch, case, default
switch (score ~/ 10) {
  case 10:
  case 9:
    print('Excellent');
    break;
  case 8:
    print('Good');
    break;
  default:
    print('Keep studying');
}

🔸 Loop Keywords

// for loop
for (int i = 0; i < 5; i++) {
  print('Count: $i');
}

// while loop
int count = 0;
while (count < 3) {
  print('While: $count');
  count++;
}

// for-in loop
List fruits = ['apple', 'banana', 'orange'];
for (String fruit in fruits) {
  print('Fruit: $fruit');
}

🔹 Class and Object Keywords

Keywords for object-oriented programming:

// abstract class
abstract class Shape {
  void draw(); // abstract method
}

// class with inheritance
class Circle extends Shape {
  double radius;
  
  Circle(this.radius);
  
  @override
  void draw() {
    print('Drawing circle with radius $radius');
  }
}

// interface implementation
class Square implements Shape {
  double side;
  
  Square(this.side);
  
  @override
  void draw() {
    print('Drawing square with side $side');
  }
}

🔹 Async Keywords

Keywords for handling asynchronous operations:

// async function returns Future
Future loadUserData() async {
  // await pauses execution until Future completes
  String userData = await fetchFromServer();
  return userData;
}

// Using async/await
void main() async {
  try {
    String data = await loadUserData();
    print('User data: $data');
  } catch (e) {
    print('Error: $e');
  }
}

Async Flow:

1. Function marked with async

2. await pauses until operation completes

3. Execution continues with result

🔹 Complete Keywords List

All Dart Keywords:

abstract - abstract class

as - type cast

assert - debug assertion

async - async function

await - wait for Future

break - exit loop

case - switch case

catch - exception handling

class - define class

const - compile constant

continue - next iteration

default - default case

do - do-while loop

else - alternative condition

enum - enumeration

extends - inheritance

false - boolean false

final - runtime constant

finally - cleanup code

for - for loop

if - condition

implements - interface

import - import library

in - for-in loop

is - type check

late - lazy initialization

new - create instance

null - null value

return - return value

static - class member

super - parent class

switch - switch statement

this - current instance

throw - throw exception

true - boolean true

try - exception handling

var - variable declaration

void - no return value

while - while loop

with - mixin