# extension_type_implements_disallowed_type

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



_Extension types can't implement '{0}'._

## Description

The analyzer produces this diagnostic when an extension type implements a
type that it isn't allowed to implement.

## Example

The following code produces this diagnostic because extension types can't
implement the type `dynamic`:

```dart
extension type A(int i) implements [!dynamic!] {}
```

## Common fixes

Remove the disallowed type from the implements clause:

```dart
extension type A(int i) {}
```

