Hi Hongbo,

As you observed, `val` can be used via inheritance to expose some private state to subclasses without exposing it to the outside.

Cheers

Nicolas

On Sat, Jul 2, 2016 at 7:02 PM, Hongbo Zhang (BLOOMBERG/ 731 LEX) <hzhang295@bloomberg.net> wrote:

Thanks for your reply. But if `val` is not accessible from outside, why it is the part of class type signature, any reason for this design?

From: gabriel.scherer@gmail.com At: 07/02/16 13:00:34

To: HONGBO ZHANG (BLOOMBERG/ 731 LEX)
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] question: what is the recommended use case of `val` in class type

Objects have some private state, and they expose methods that can be called from the outside. "val" fields correspond to such private state, they are not accessible from outside and are thus not part of an object's type.

You can always expose a value field to the outside through a "getter" method to access it (and a "setter" method to mutate it if relevant), but that is often considered dubious object-oriented style -- it tends to go against good encapsulation.

On Sat, Jul 2, 2016 at 12:45 PM, Hongbo Zhang (BLOOMBERG/ 731 LEX) <hzhang295@bloomberg.net> wrote:

Dear all,

I have a question about val in class type, is it only useful in inheritance?

for example

class type text = object val mutable text : string end

let f (x : text ) = x#text;;

^

Error: This expression has type text

It has no method text

Thanks -- Hongbo