# deprecated_extend

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



_Extending '{0}' is deprecated._

## Description

The analyzer produces this diagnostic when a class annotated with
`@Deprecated.extend` is used in the `extends` clause of a class
declaration.

This annotation indicates that the ability to extend the annotated class
is deprecated and will soon be removed. This change will likely be
enforced by marking the class with `interface`, `final`, or `sealed`.

## Example

If the library `p` defines a class annotated with `@Deprecated.extend`:

```dart
@Deprecated.extend()
class C {}
```

Then, in any library other than `p`, the following code produces this
diagnostic:

```dart
import 'package:p/p.dart';

class D extends [!C!] {}
```

## Common fixes

Follow any directions found in the `Deprecation.extend` annotation.
Otherwise, remove the `extends` clause.

```dart
class D {}
```

