Dart Enums

Key Enum Concepts

enum Status { pending, approved, rejected }

Status.pending.index // 0

Status.approved.name // 'approved'

switch (status) {
  case Status.pending: break;
}

🔹 Basic Enum Usage

Here's how to create and use simple enums:

// Define an enum for days of the week
enum Day {
  monday,
  tuesday,
  wednesday,
  thursday,
  friday,
  saturday,
  sunday
}

void main() {
  // Using enum values
  Day today = Day.friday;
  Day weekend = Day.saturday;
  
  print('Today is: ${today.name}');        // Today is: friday
  print('Index of today: ${today.index}'); // Index of today: 4
  
  // Get all enum values
  print('All days: ${Day.values}');
  
  // Check enum equality
  if (today == Day.friday) {
    print('TGIF! It\'s Friday!');
  }
  
  // Using in switch statement
  switch (today) {
    case Day.monday:
      print('Start of work week');
      break;
    case Day.friday:
      print('End of work week');
      break;
    case Day.saturday:
    case Day.sunday:
      print('Weekend!');
      break;
    default:
      print('Midweek day');
  }
}

🔹 Enhanced Enums with Methods

Dart allows enums to have methods, properties, and constructors:

enum Planet {
  mercury(3.303e+23, 2.4397e6),
  venus(4.869e+24, 6.0518e6),
  earth(5.976e+24, 6.37814e6),
  mars(6.421e+23, 3.3972e6);

  // Constructor
  const Planet(this.mass, this.radius);

  // Properties
  final double mass;       // in kilograms
  final double radius;     // in meters

  // Method to calculate surface gravity
  double get surfaceGravity => 6.67300E-11 * mass / (radius * radius);
  
  // Method to calculate weight on this planet
  double calculateWeight(double earthWeight) {
    return earthWeight * surfaceGravity / Planet.earth.surfaceGravity;
  }
  
  // Override toString for better display
  @override
  String toString() => 'Planet: ${name.toUpperCase()}';
}

void main() {
  double earthWeight = 70.0; // kg
  
  print('Weight on different planets:');
  for (Planet planet in Planet.values) {
    double weight = planet.calculateWeight(earthWeight);
    print('${planet}: ${weight.toStringAsFixed(2)} kg');
  }
  
  // Access specific planet properties
  Planet earth = Planet.earth;
  print('\nEarth details:');
  print('Mass: ${earth.mass} kg');
  print('Radius: ${earth.radius} m');
  print('Surface Gravity: ${earth.surfaceGravity.toStringAsFixed(2)} m/s²');
}

🔹 Enum with String Values

Create enums that work with specific string values:

enum HttpStatus {
  ok(200, 'OK'),
  notFound(404, 'Not Found'),
  internalServerError(500, 'Internal Server Error'),
  badRequest(400, 'Bad Request');

  const HttpStatus(this.code, this.message);

  final int code;
  final String message;

  // Static method to find status by code
  static HttpStatus? fromCode(int code) {
    for (HttpStatus status in HttpStatus.values) {
      if (status.code == code) {
        return status;
      }
    }
    return null;
  }

  // Check if status indicates success
  bool get isSuccess => code >= 200 && code < 300;
  
  // Check if status indicates error
  bool get isError => code >= 400;

  @override
  String toString() => '$code: $message';
}

void main() {
  // Using enum with custom values
  HttpStatus response = HttpStatus.ok;
  print('Response: $response');              // Response: 200: OK
  print('Is success: ${response.isSuccess}'); // Is success: true
  print('Is error: ${response.isError}');     // Is error: false

  // Find status by code
  HttpStatus? status = HttpStatus.fromCode(404);
  if (status != null) {
    print('Found status: $status');          // Found status: 404: Not Found
  }

  // Handle different status codes
  void handleResponse(HttpStatus status) {
    switch (status) {
      case HttpStatus.ok:
        print('✅ Request successful');
        break;
      case HttpStatus.notFound:
        print('❌ Resource not found');
        break;
      case HttpStatus.internalServerError:
        print('💥 Server error occurred');
        break;
      default:
        print('⚠️ Other status: $status');
    }
  }

  handleResponse(HttpStatus.notFound);       // ❌ Resource not found
  handleResponse(HttpStatus.ok);             // ✅ Request successful
}