Is it possible to switch named constructors in Dart?-CodePudding

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';
}

CodePudding user response：

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