field_initializer_factory_constructor

Initializing formal parameters can't be used in factory constructors.

The analyzer produces this diagnostic when a factory constructor has an initializing formal parameter. Factory constructors can't assign values to fields because no instance is created; hence, there is no field to assign.

The following code produces this diagnostic because the factory constructor uses an initializing formal parameter:

class C {
  int? f;

  factory C(this.f) => throw 0;
}

Replace the initializing formal parameter with a normal parameter:

class C {
  int? f;

  factory C(int f) => throw 0;
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.