redirect_to_type_alias_expands_to_type_parameter

A redirecting constructor can't redirect to a type alias that expands to a type parameter.

The analyzer produces this diagnostic when a redirecting factory constructor redirects to a type alias, and the type alias expands to one of the type parameters of the type alias. This isn't allowed because the value of the type parameter is a type rather than a class.

The following code produces this diagnostic because the redirect to B<A> is to a type alias whose value is T, even though it looks like the value should be A:

class A implements C {}

typedef B<T> = T;

abstract class C {
  factory C() = B<A>;
}

Use either a class name or a type alias that is defined to be a class rather than a type alias defined to be a type parameter:

class A implements C {}

abstract class C {
  factory C() = A;
}

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.