The :protection option for EIEIO slots

The :protection option for EIEIO slots

[Stefan Monnier]

Hi Eric,

Can you give me some background on the :protection option for the slots
of EIEIO objects?  This doesn't exist in CLOS, so I'm wondering what
were the motivations to add them.

According to my grepping, the `private' setting is only used in the
eieio-tests.  And the `protected' setting is used at a few places, but
it's been implemented wrong so you can do:

  (defmethod foo ((x class-1))
    (slot-value <any-object> <any-protected-slot>))

and the access will be allowed, even though only protected slots
belonging to class-1 (or its superclasses) should be granted access.
This is because the code was the check was:

         ((and (eq (cdr fsym) 'protected)
               (eieio--scoped-class)
               (or (child-of-class-p class (eieio--scoped-class))
 		   (and (eieio-object-p obj)
                        (child-of-class-p class (eieio--object-class-object obj)))))


Which can be (and has been) rewritten to:

         ((and (eq (cdr fsym) 'protected)
               (eieio--scoped-class)
               (or (child-of-class-p class (eieio--scoped-class))
                   (and (eieio-object-p obj)
                        (progn
                          (cl-assert (eq class (eieio--object-class-object obj)))
                          t))))

Since all callers of the function guarantee that the assertion won't fail.

So I'm tempted to just drop this functionality.  Any thoughts?


        Stefan

Re: The :protection option for EIEIO slots

[Eric Ludlam]

On 01/15/2015 10:00 PM, Stefan Monnier wrote:
> Hi Eric,
>
> Can you give me some background on the :protection option for the slots
> of EIEIO objects?  This doesn't exist in CLOS, so I'm wondering what
> were the motivations to add them.
>
As far as I remember, I was learning C++ at the time and using Emacs to 
teach myself OO concepts and thought it would be useful.  I didn't 
hesitate much about extending CLOS.

I'm surprised the protected slot doesn't work.  There is a test for that 
throwing an error.

>
> So I'm tempted to just drop this functionality.  Any thoughts?
>

No flags.  I've written a lot of classes and apparently didn't use it 
very much, so feel free.

Eric

Re: The :protection option for EIEIO slots

[Stefan Monnier]

> I'm surprised the protected slot doesn't work.  There is a test for that
> throwing an error.

The test checks that you can't access a protected slot from outside of
a method.  But as soon as you're inside a method that dispatched on
a class (i.e. when eieio--scoped-class is non-nil), you can access
any protected slot of any object of any class.

> No flags.  I've written a lot of classes and apparently didn't use it very
> much, so feel free.

Good, thanks,


        Stefan