prefer_abstract_final_static_class

v0.3.0 Warning Fix Code Organization

Flags classes that contain only static members but are not declared as abstract final. Without these modifiers, a static-only class can be accidentally instantiated or subclassed, which is almost never the intended use.

Why use this rule

Marking a static-only class as abstract final makes the intent clear: it is a namespace for constants or utility functions, not something to instantiate or extend. This prevents misuse and documents the design decision directly in the class declaration.

See also: Dart language - Abstract classes | Dart language - Final classes

Don’t

class BadConstants {
  static const pi = 3.14159;
  static const e = 2.71828;
}

class BadUtils {
  static String greet(String name) => 'Hello, $name!';
  static int add(int a, int b) => a + b;
}

Do

abstract final class GoodConstants {
  static const pi = 3.14159;
  static const e = 2.71828;
}

abstract final class GoodUtils {
  static String greet(String name) => 'Hello, $name!';
  static int add(int a, int b) => a + b;
}

// Classes with instance members are fine:
class MixedClass {
  final String name;
  MixedClass(this.name);
  static const defaultName = 'World';
}

// Classes with constructors are fine:
class WithConstructor {
  WithConstructor._();
  static const value = 42;
}

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      prefer_abstract_final_static_class: false