static_duck_typing.ml

#! /usr/bin/env ocaml


type some_interface = <
  foo : unit -> unit
>

let do_stuff (p : some_interface) =
  p#foo ()



class class_a = object (self)
  method foo () = ()
end

let () =
  do_stuff (new class_a)



class class_b = object (self)
  method not_foo () = ()
end

let () =
  do_stuff (new class_b)  (* Compile-time error *)