supertype_expands_to_type_parameter

A type alias that expands to a type parameter can't be implemented.

A type alias that expands to a type parameter can't be mixed in.

A type alias that expands to a type parameter can't be used as a superclass constraint.

A type alias that expands to a type parameter can't be used as a superclass.

The analyzer produces this diagnostic when a type alias that expands to a type parameter is used in an extends, implements, with, or on clause.

The following code produces this diagnostic because the type alias T, which expands to the type parameter S, is used in the extends clause of the class C:

typedef T<S> = S;

class C extends T<Object> {}

Use the value of the type argument directly:

typedef T<S> = S;

class C extends Object {}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.