CODEWITHSUNDEEP
flutterdartenums
spydon
spydon

Reputation: 11592

Use enum constructor directly in Dart

Is it possible to use the enum constructor directly?

void main() {
  print(Test(1));
}

enum Test {
  test1(1),
  test2(2);
  
  final int id;

  const Test(this.id);
}

This will give the following error:

generative enum constructors can only be used as targets of redirection

I know that it can be solved like this:

enum Test {
  test1(1),
  test2(2);

  final int id;

  const Test(this.id);
  
  factory Test.fromId(int id) {
    return values.firstWhere((e) => e.id == id);
  }
}

But it feels like there must be a way to avoid this boiler plate factory?

Upvotes: 16

Views: 7522

Answers (2)

shiroyoru
shiroyoru

Reputation: 11

While it seems to be necessary to use factory, you can have your factory to be unnamed and use a named constructor inside the class, and therefore "looks easier" when using the enum factory.

enum Test {
  error._inner(0),
  test1._inner(1),
  test2._inner(2);

  final int id;

  const Test._inner(this.id);
  
  factory Test(int id) {
    return values.firstWhere((e) => e.id == id, orElse:()=>error);
  }
}

Upvotes: 1

Ivo
Ivo

Reputation: 23357

I don't think there is an easier way than that factory. My personal opinion is also that it really isn't that much of boiler plate, but that's subjective.

One reason I can think of why there isn't an easier method, is because the id in your case is not unique, this is perfectly valid:

enum Test {
  test1(1),
  secondtest1(1),
  test2(2);

  final int id;

  const Test(this.id);
  
  factory Test.fromId(int id) {
    return values.firstWhere((e) => e.id == id);
  }
}

Now you will never be able to get the secondtest1 using the fromId

Upvotes: 28

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