invalid_factory_method_impl

Factory method '{0}' doesn't return a newly allocated object.

The analyzer produces this diagnostic when a method that is annotated with the factory annotation doesn't return a newly allocated object.

The following code produces this diagnostic because the method createC returns the value of a field rather than a newly created instance of C:

import 'package:meta/meta.dart';

class Factory {
  C c = C();

  @factory
  C createC() => c;
}

class C {}

Change the method to return a newly created instance of the return type:

import 'package:meta/meta.dart';

class Factory {
  @factory
  C createC() => C();
}

class C {}

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.