Dart
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.
Exercise 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.
Show example solution
enum Heat { low(10), medium(25), high(40); final int degrees; const Heat(this.degrees); }
void main() {
print(Heat.medium.degrees);
}
Test yourself
-
What does an enhanced enum support?
- Only methods
- Fields and a constructor
- Only a name
- Only an index
Show answer
Only methods — An enhanced enum supports fields and a constructor.
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The const constructor
enum Heat { low(10), medium(25), high(40); final int degrees; ____ Heat(this.degrees); }
Show answer
enum Heat { low(10), medium(25), high(40); final int degrees; const Heat(this.degrees); }
-
Match enhanced enum conditions
- const constructor
- is required
- final field
- immutable data
- semicolon
- after the constant list
- method
- computed behavior
Next lesson: switch with enum
