| library; | 
 | // | 
 | // Problems in library: | 
 | // | 
 | // pkg/front_end/testcases/general/issue47728_4.dart:9:11: Error: The type 'A' which is an alias of 'dynamic Function()?' can't be used as supertype because it is nullable. | 
 | // class C = A with B; | 
 | //           ^ | 
 | // pkg/front_end/testcases/general/issue47728_4.dart:5:9: Context: The issue arises via this type alias. | 
 | // typedef A = Function()?; | 
 | //         ^ | 
 | // | 
 | import self as self; | 
 | import "dart:core" as core; | 
 |  | 
 | typedef A = () →? dynamic; | 
 | abstract class B extends core::Object /*isMixinDeclaration*/  { | 
 | } | 
 | class C = core::Object with self::B { | 
 |   synthetic constructor •() → self::C | 
 |     : super core::Object::•() | 
 |     ; | 
 | } | 
 | static method main() → dynamic {} |