CopyWith to allow setting values to null - like spread operator

[brianegan]

CopyWith to allow setting values to null - like spread operator

[atreeon]

This would work but maybe there is a more succinct and descriptive method.

void main() {
  var bob2 = new Person2(age: 15, name: 'Bob');
  print(bob2.toString());

  var joe2 = bob2.copyWith(name: new Nullable<String>(null));
  print(joe2.toString());
}

class Person2 {
  final int age;
  final String name;

  Person2({this.age, this.name});

  Person2 copyWith({Nullable<int> age, Nullable<String> name}) {
    return new Person2(
      age: age == null ? this.age : age.value,
      name: name == null ? this.name : name.value,
    );
  }

  @override
  String toString() {
    return 'age: $age, name: $name';
  }
}

class Nullable<T> {
  T _value;

  Nullable(this._value);

  T get value {
    return _value;
  }
}

[brianegan]

Yah, I really hope they even get "data classes" like Kotlin, which would make this type-safe and easy. Please let me know if I can help further!

[atreeon]

That works a little nicer than my Nullable. I do love the javascript spread operator for this kind of thing though...I wonder if there was a way the Dart team could implement something like this (I'm guessing no due to the typed quality of the lanaguage...it does make my code nice and concise...I still prefer dart to js though!)

[brianegan]

Hey there -- yep, in this case, you'd need an extra class like the one you've proposed. You can either create a class just as you've done, or consider using the Optional class from the quiver library: https://pub.dartlang.org/packages/quiver

[pumuckelo]

Hi @brianegan , I just stumbled on the same problem and randomly found the solution to why my state isn't updating by randomly reading the copyWith Function.

What do you think of if we add a warning or information to the example of flutter_redux where the copyWith Method is shown? It's easier for other people then

[lukas-pierce]

class Nullable {
T _value;

Nullable(this._value);

T get value {
return _value;
}
}

class Nullable<T> {
  final T? _value;

  const Nullable(this._value);

  T? get value => _value;
}