prefer-declaring-const-constructor

added in: 1.0.0

performance

⚙️🛠

preset: recommended

Warns when a class with no non-final fields has a non-constant constructor declaration.

Additional resources:

• https://github.com/dart-lang/linter/issues/3983
• https://stackoverflow.com/a/57618161
• https://medium.com/nerd-for-tech/flutter-performance-analysis-of-const-constructor-d2a72fd8a043

⚙️ Config

Set allow-one (default is false) to allow at least one const constructor.

Set ignore-abstract (default is true) to highlight abstract and sealed classes.

dart_code_metrics:
  ...
  rules:
    ...
    - prefer-declaring-const-constructor:
        allow-one: true

Example

❌ Bad:

// LINT
class MyException implements Exception {}

class Square {
  Square(this.sideLength); // LINT

  Square.fromRadius(double radius) : sideLength = 2 * radius; // LINT

  final double sideLength;
}

class Square {
  Square(this.sideLength, this.color); // LINT

  final double sideLength;
  final Color color;
}

✅ Good:

class MyException implements Exception {
  const MyException();
}

class Square {
  const Square(this.sideLength);

  const Square.fromRadius(double radius) : sideLength = 2 * radius;

  final double sideLength;
}

class Square {
  const Square(this.sideLength, this.color);

  final double sideLength;
  final Color color;
}