Re: [Caml-list] OO design

["Remi Vanicat" <remi.vanicat@gmail.com>]

2006/5/5, David Baelde <david.baelde@gmail.com>:
> Hi,
>
> I'm no OO guru, so my question may be irrelevant, or there just might
> not be an answer, which wouldn't hurt..
>
> Let's say that I have a base class, with some kind of activation
> procedure: anybody wanting to use the class must call #enter before,
> and then call #leave for releasing. Internally, the methods #do_enter
> and #do_leave are called respectively at the first #enter and last
> #leave.
>
> Nobody should call the #do_* directly, and I'd also like to make sure
> the #enter and #leave are never overriden, since their behaviour is
> important and actually much more complex than what I said.

If the solution given Gerd Stolpmann have the problem to disallow the
inheritence, I've another that make ineritence and overriding enter
and leave possible, but ensure that method that overide enter and
leave do call the old enter and leave :

struct
  type enter = unit
  type leave = unit
  class foo =
     method enter ... : enter = ....
     method leave ....: leave = ...
     ....
   end
end : sig
  type enter
  type leave
  class foo :
    method enter : ... -> enter
    method leave : ... -> leave
  end
end

after this, the only way to produce an object of type enter is to call
the original enter method (same for leave). And as method that overide
enter must have the same type, the have to call the enter method to
have it (well, there might be other way, but the user of the method
have to make thing complicated for this).

Another plus of this method of doing it is that if you haev e method of type
  method bar : enter -> unit
then one can only call it if he had call previously the enter method.