prefer_initializing_formals

Use initializing formals when possible.

This rule is available as of Dart 2.0.0.

Rule sets: recommended, flutter

This rule has a quick fix available.

DO use initializing formals when possible.

Using initializing formals when possible makes your code more terse.

BAD:

class Point {
  num x, y;
  Point(num x, num y) {
    this.x = x;
    this.y = y;
  }
}

GOOD:

class Point {
  num x, y;
  Point(this.x, this.y);
}

BAD:

class Point {
  num x, y;
  Point({num x, num y}) {
    this.x = x;
    this.y = y;
  }
}

GOOD:

class Point {
  num x, y;
  Point({this.x, this.y});
}

NOTE: This rule will not generate a lint for named parameters unless the parameter name and the field name are the same. The reason for this is that resolving such a lint would require either renaming the field or renaming the parameter, and both of those actions would potentially be a breaking change. For example, the following will not generate a lint:

class Point {
  bool isEnabled;
  Point({bool enabled}) {
    this.isEnabled = enabled; // OK
  }
}

NOTE: Also note that it is possible to enforce a type that is stricter than the initialized field with an initializing formal parameter. In the following example the unnamed Bid constructor requires a non-null int despite amount being declared nullable (int?).

class Bid {
 final int? amount;
 Bid(int this.amount);
 Bid.pass() : amount = null;
}

To enable the prefer_initializing_formals rule, add prefer_initializing_formals under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - prefer_initializing_formals