Re: [Caml-list] question: what is the recommended use case of `val` in class type

[Nicolas Ojeda Bar <nicolas.ojeda.bar@lexifi.com>]

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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) <hzhang295@bloomberg.net>
> 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
>> <#m_1963343833435410216_m_-4902517353790339526_text>;;
>> ^
>> Error: This expression has type text
>> It has no method text
>> Thanks -- Hongbo
>>
>
>

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