instantiate_type_alias_expands_to_type_parameter

Type aliases that expand to a type parameter can't be instantiated.

The analyzer produces this diagnostic when a constructor invocation is found where the type being instantiated is a type alias for one of the type parameters of the type alias. This isn't allowed because the value of the type parameter is a type rather than a class.

The following code produces this diagnostic because it creates an instance of A, even though A is a type alias that is defined to be equivalent to a type parameter:

typedef A<T> = T;

void f() {
  const A<int>();
}

Use either a class name or a type alias defined to be a class, rather than a type alias defined to be a type parameter:

typedef A<T> = C<T>;

void f() {
  const A<int>();
}

class C<T> {
  const C();
}

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.