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