invalid_use_of_type_outside_library
The class '{0}' can't be extended outside of its library because it's a final class.
The class '{0}' can't be extended outside of its library because it's an interface class.
The class '{0}' can't be extended, implemented, or mixed in outside of its library because it's a sealed class.
The class '{0}' can't be implemented outside of its library because it's a base class.
The class '{0}' can't be implemented outside of its library because it's a final class.
The class '{0}' can't be used as a mixin superclass constraint outside of its library because it's a final class.
The mixin '{0}' can't be implemented outside of its library because it's a base mixin.
Description
#The analyzer produces this diagnostic when an extends
, implements
, with
, or on
clause uses a class or mixin in a way that isn't allowed given the modifiers on that class or mixin's declaration.
The message specifies how the declaration is being used and why it isn't allowed.
Example
#Given a file a.dart
that defines a base class A
:
base class A {}
The following code produces this diagnostic because the class B
implements the class A
, but the base
modifier prevents A
from being implemented outside of the library where it's defined:
import 'a.dart';
final class B implements A {}
Common fixes
#Use of this type is restricted outside of its declaring library. If a different, unrestricted type is available that can provide similar functionality, then replace the type:
class B implements C {}
class C {}
If there isn't a different type that would be appropriate, then remove the type, and possibly the whole clause:
class B {}
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.