Skip to main content

prefer-declaring-const-constructor

added in: 1.0.0
warning
⚙️🛠
Pro+
preset: recommended

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

Declaring const class constructors allows creating const instances and it's usually preferable to declare const constructors everywhere possible.

⚙️ Config​

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

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

analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-declaring-const-constructor:
        allow-one: false
        ignore-abstract: true

Example​

❌ Bad:

// LINT: Prefer declaring a const constructor.
class MyException implements Exception {}

class Square {
  Square(this.sideLength); // LINT: Prefer declaring a const constructor.

  // LINT: Prefer declaring a const constructor.
  Square.fromRadius(double radius) : sideLength = 2 * radius;

  final double sideLength;
}

class Square {
  // LINT: Prefer declaring a const constructor.
  Square(this.sideLength, this.color);

  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;
}

Example with "allow-one"​

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

✅ Good:

class Square {
  const Square(this.sideLength);

  // Correct, already has one const constructor
  Square.fromRadius(double radius) : sideLength = 2 * radius;

  final double sideLength;
}

Example with "ignore-abstract"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-declaring-const-constructor:
        ignore-abstract: false

❌ Bad:

// LINT: Prefer declaring a const constructor.
abstract interface class Extended { }

Additional Resources​