mixin_application_not_implemented_interface

'{0}' can't be mixed onto '{1}' because '{1}' doesn't implement '{2}'.

The analyzer produces this diagnostic when a mixin that has a superclass constraint is used in a mixin application with a superclass that doesn't implement the required constraint.

The following code produces this diagnostic because the mixin M requires that the class to which it's applied be a subclass of A, but Object isn't a subclass of A:

class A {}

mixin M on A {}

class X = Object with M;

If you need to use the mixin, then change the superclass to be either the same as or a subclass of the superclass constraint:

class A {}

mixin M on A {}

class X = A with M;

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.