prefer_constructors_over_static_methods

PREFER defining constructors instead of static methods to create instances.

In most cases, it makes more sense to use a named constructor rather than a static method because it makes instantiation clearer.

BAD:

class Point {
  num x, y;
  Point(this.x, this.y);
  static Point polar(num theta, num radius) {
    return Point(radius * math.cos(theta),
        radius * math.sin(theta));
  }
}

GOOD:

class Point {
  num x, y;
  Point(this.x, this.y);
  Point.polar(num theta, num radius)
      : x = radius * math.cos(theta),
        y = radius * math.sin(theta);
}