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Enhanced enums

Learn Dart 3 enhanced enums.

Enhanced enum

Dart 3 introduced enhanced enum. In addition to constants you can add fields, constructors and methods. So each constant carries its own data. A classic enum holds only a name; an enhanced enum holds name plus value.

Example: enum Heat { low(10), medium(25), high(40); final int degrees; const Heat(this.degrees); }. Each constant gets a degrees field; Heat.medium.degrees gives 25. The constructor must be const; otherwise you get a compile error. This lets you treat constants like real types.

Fields and methods

To add fields to an enhanced enum, place a semicolon after the constant list and then the field definitions. enum Distance { near(5), far(50); final int km; const Distance(this.km); int get meters => km * 1000; }. Here meters is a computed getter.

Each constant can access these fields and methods: Distance.far.meters gives 50000. So the enum is not just a label but a type carrying real behavior. The conditions are: the constructor must be const, all fields must be final, and a semicolon after the constant list is required.

Practice Your turn: enum with a degrees field

Define an enhanced enum Heat with constants low(10), medium(25), high(40). Add a final int degrees field and a const Heat(this.degrees) constructor. In main print Heat.medium.degrees.

Starter code

main.dart
void main() {
  // Define the Heat enhanced enum
  // Print a constant's degrees field
}

Sample solution

main.dart
enum Heat { low(10), medium(25), high(40); final int degrees; const Heat(this.degrees); }

void main() {
  print(Heat.medium.degrees);
}

Expected output

25

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does an enhanced enum support?

  • Only methods Correct answer
  • Fields and a constructor
  • Only a name
  • Only an index

Explanation: An enhanced enum supports fields and a constructor.

2 The const constructor

Question 
enum Heat { low(10), medium(25), high(40); final int degrees; ____ Heat(this.degrees); }
Answer 
enum Heat { low(10), medium(25), high(40); final int degrees; const Heat(this.degrees); }

Explanation: An enhanced enum constructor must be const.

3 Match enhanced enum conditions

Term Meaning
const constructor is required
final field immutable data
semicolon after the constant list
method computed behavior

All lessons in Beginner

1 Dart basics

  1. What is Dart?
  2. Your first program
  3. dart run
  4. Comments
  5. String interpolation
  6. Summary - Dart basics

2 Variables

  1. var and type
  2. final
  3. const
  4. late
  5. Null safety
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and String
  4. Type inference
  5. dynamic
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Null-aware operators
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String interpolation
  3. length and methods
  4. substring
  5. contains and indexOf
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Pattern matching
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. for-in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Lists

  1. Creating lists
  2. List access
  3. add and remove
  4. length and contains
  5. List methods
  6. Summary - Lists

11 Sets and Maps

  1. Set
  2. Set operations
  3. Map
  4. Map operations
  5. Map iteration
  6. Summary - Sets and Maps

12 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Optional parameters
  5. First-class functions
  6. Summary - Functions

13 Null safety in depth

  1. Nullable types
  2. Null-aware operators
  3. The ! operator
  4. late
  5. Null check
  6. Summary - Null safety

14 Class basics

  1. class
  2. Constructor
  3. Instance variables
  4. Methods
  5. this
  6. Summary - Class basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. split and join
  2. replace
  3. trim and pad
  4. RegExp
  5. StringBuffer
  6. Summary - Advanced strings

17 Enums

  1. Defining enums
  2. Enum values
  3. Enhanced enums
  4. switch with enum
  5. Enum and patterns
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. The Exception class
  5. on clause
  6. Summary - Exceptions

19 Async basics

  1. Future
  2. async/await
  3. then
  4. Future.error
  5. Future.wait
  6. Summary - Async basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together