Yes I can't quite remember why I couldn't get it to work. I want to make something where this is valid, but couldn't manage it:

    def foo() -> OneOf[Bar, Baz]:
      if blah():
        return Bar()
      return Baz()

   

   def bar_to_blah(bar:Bar) -> Blah :
     ...

   def baz_to_blah(baz:Baz) -> Blah :
     ...


   one_of_bar_or_baz = foo()
   blah = one_of_bar_or_baz.match(bar_to_blah, baz_to_blah) 

but the critical thing is to get a type error if you add another case to foo's return type, or change the generics to different types.