# mixin_application_not_implemented_interface

> Details about the mixin_application_not_implemented_interface diagnostic produced by the Dart analyzer.



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

## Description

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.

## Example

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`:

```dart
class A {}

mixin M on A {}

class X = Object with [!M!];
```

## Common fixes

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

```dart
class A {}

mixin M on A {}

class X = A with M;
```

[mixin application]: /resources/glossary#mixin-application

