extension_type_implements_itself

The extension type can't implement itself.

The analyzer produces this diagnostic when an extension type implements itself, either directly or indirectly.

The following code produces this diagnostic because the extension type A directly implements itself:

extension type A(int i) implements A {}

The following code produces this diagnostic because the extension type A indirectly implements itself (through B):

extension type A(int i) implements B {}

extension type B(int i) implements A {}

Break the cycle by removing a type from the implements clause of at least one of the types involved in the cycle:

extension type A(int i) implements B {}

extension type B(int i) {}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.