sort_constructors_first  
            
            Sort constructor declarations before other members.
This rule is available as of Dart 2.0.0.
This rule has a quick fix available.
Details
DO sort constructor declarations before other members.
BAD:
abstract class Visitor {
  double value;
  visitSomething(Something s);
  Visitor();
}
GOOD:
abstract class Animation<T> {
  const Animation(this.value);
  double value;
  void addListener(VoidCallback listener);
}
Usage
To enable the sort_constructors_first rule,
add sort_constructors_first under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - sort_constructors_first