module Mod def foo [42, super(:sym)] end end class Foo prepend Mod def foo(sym_arg) sym_arg.to_s end def bar foo end end __END__ # Errors smoke/prepend1.rb:3: [error] no superclass method: Mod#foo # Classes module Mod def foo: -> ([Integer, String | untyped]) end class Foo prepend Mod def foo: (:sym | untyped sym_arg) -> (String | untyped) def bar: -> ([Integer, String | untyped]) end