prefer_mixin

Prefer using mixins.

Dart 2.1 introduced a new syntax for mixins that provides a safe way for a mixin to invoke inherited members using super. The new style of mixins should always be used for types that are to be mixed in. As a result, this lint will flag any uses of a class in a with clause.

BAD:

class A {}
class B extends Object with A {}

OK:

mixin M {}
class C with M {}

To enable the prefer_mixin rule, add prefer_mixin under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - prefer_mixin

If you're instead using the YAML map syntax to configure linter rules, add prefer_mixin: true under linter > rules:

linter:
  rules:
    prefer_mixin: true