Initialize this to a final variable in dart

Question

I want to initialize a final variable in a class to this.

Class C{
  final int variable1 = 0; //dynamically generated value
  final int variable2;

  C(): this.variable2 = this.variable1 + 1; //variable2 need access to "this" to initialize

}

Answer 1

You could use a private constructor with a public factory constructor.

class C {
  final int variable1;
  final int variable2;

  C._(this.variable1, this.variable2);

  factory C() {
    var v1 = Random().nextInt(10);
    return C._(v1, v1 + 1);
  }

  @override
  String toString() => 'Instance of C $variable1 $variable2';
}

Answer 2

With regard to the API of your class, a final member variable is not really any different from providing a getter. Since you want variable2 to never be reassigned and to be based on variable1 , it could exist solely as a getter:

class C {
  final int variable1 = 0;
  int get variable2 => variable1 + 1;

  ...
}

If you don't want to repeat the computation every time variable2 is accessed, you could use a private member variable with a public getter:

class C {
  final int variable1 = 0;

  int get variable2 => _variable2;
  int _variable2;

  C() {
    _variable2 = variable1 + 1;
  }
}