CODEWITHSUNDEEP
flutterdartoop
Bugzilla
Bugzilla

Reputation: 2506

Is it possible to switch named constructors in Dart?

Is it possible to have dataful named contructors like Animal.dog() and Animal.cat() and an utility named constructor like Animal.specie() used to switch between dataful named constructors?

I came up with this because I find myself writing long switches in the middle on Widgets and I think hiding this inside the class definition would be better. Probably there is an OOP concept I'm missing here, so if there is an easier solution I don't see please, let me know.

enum AnimalsEnum { dog, cat }

class Animal {
  final int age;
  final String data;
  final AnimalsEnum specie;

  Animal(this.age, this.data, this.specie);

  Animal.bySpecie(this.age, this.specie) {
    switch (specie) {
      case AnimalsEnum.dog:
        this = Animal._dog(this.age); // Does not work
        break;
      case AnimalsEnum.cat:
        this = Animal._cat(this.age); // Does not work
        break;
    }
  }

  Animal._dog(this.age)
      : specie = AnimalsEnum.dog,
        data = 'Dogs love Flutter';
  Animal._cat(this.age)
      : specie = AnimalsEnum.cat,
        data = 'Cats love pasta';
}

Upvotes: 0

Views: 386

Answers (1)

Guillaume Roux
Guillaume Roux

Reputation: 7308

Yes you can easily obtain this result by using a factory constructor.

Code

class Animal {
  final int age;
  final String data;
  final AnimalsEnum specie;

  Animal({required this.age, required this.data, required this.specie});

  factory Animal.dog(int age) {
    return Animal(
      age: age,
      data: 'Dogs love Flutter',
      specie: AnimalsEnum.dog,
    );
  }

  factory Animal.cat(int age) {
    return Animal(
      age: age,
      data: 'Cats love pasta',
      specie: AnimalsEnum.cat,
    );
  }

  factory Animal.bySpecie({
    required int age,
    required AnimalsEnum specie,
  }) {
    switch (specie) {
      case AnimalsEnum.dog:
        return Animal.dog(age);
      case AnimalsEnum.cat:
        return Animal.cat(age);
    }
  }
}

Example

void main() {
  final cat = Animal.cat(1);
  final dog = Animal.dog(2);
  final specie = Animal.bySpecie(age: 3, specie: AnimalsEnum.cat);
  
  print('${cat.age} - ${cat.data} - ${cat.specie}');
  print('${dog.age} - ${dog.data} - ${dog.specie}');
  print('${specie.age} - ${specie.data} - ${specie.specie}');
}

Output

1 - Cats love pasta - AnimalsEnum.cat
2 - Dogs love Flutter - AnimalsEnum.dog
3 - Cats love pasta - AnimalsEnum.cat

Try the example on DartPad

Upvotes: 1

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