[armedbear-devel] class-prototype

[Blake McBride]

BTW, my CLOS utilities make this and other CLOS usage very easy.  It
also includes a tutorial.  See:

http://blake.mcbride.name/software/clos-utils/index.html

Blake McBride


On Wed, Mar 10, 2010 at 1:32 PM, Blake McBride <blake at mcbride.name> wrote:
> Here is how to do it in SBCL.  cv? represent class variables.  iv?
> represent instance variables.  Both associated to the "class1" class.
>
> (defclass meta-class1 (standard-class)
>  (cv1 cv2 cv3)
>  (:metaclass standard-class))
>
> (defmethod sb-mop:validate-superclass ((class meta-class1) (superclass
> standard-class)) t)
>
> (defclass class1 (standard-object)
>  (iv1 iv2 iv3)
>  (:metaclass meta-class1))
>
> (setf (slot-value (find-class 'class1) 'cv2) 'hello)
>
> (slot-value (find-class 'class1) 'cv2)
>
>
> Blake McBride
>
>
>
> On Wed, Mar 10, 2010 at 1:11 PM, Alessio Stalla <alessiostalla at gmail.com> wrote:
>> On Wed, Mar 10, 2010 at 6:43 PM, Alan Ruttenberg
>> <alanruttenberg at gmail.com> wrote:
>>> Hi,
>>>
>>> Thanks for adding class-prototype. Unfortunately I realize that the
>>> specification doesn't guarantee the behavior I was looking for, so I
>>> though I would solicit advise.
>>>,
>>> Basically I want to be able to access class-allocated slot values
>>> before I create any real instances. I thought I could grab the class
>>> prototype and do slot value on them, but according to the doc below
>>> initialize is not called, which I guess is when class-allocated slots
>>> are being set up.
>>>
>>> Is there a portable way of asking for the values of class slots absent
>>> the creation of at least one initialized instance?
>>
>> I'm afraid there isn't, because all slots (both instance- and
>> class-allocated) are initialized by shared-initialize, as part of the
>> instance initialization protocol[1]. Also note that, as you posted,
>> according to AMOP "The results are undefined if a portable program
>> modifies the binding of any slot of prototype instance", so
>> initializing its slots in any way, even class-allocated ones, is not
>> portable. You should use mop::allocate-instance instead of
>> class-prototype. For the record, in ABCL the two are equivalent, but
>> e.g. in SBCL they aren't (the class prototype is cached).
>>
>> AFAIK, class-prototype is only useful when you have to call a method
>> specialized on a class C, but which does not use the object of class C
>> in any way except for actually selecting the correct method. With
>> class-prototype, you have an option to call such a method even without
>> an instance of C available.
>>
>> Alessio
>>
>> [1] http://www.lispworks.com/documentation/HyperSpec/Body/f_shared.htm
>>
>>> -Alan
>>>
>>>
>>> http://www.franz.com/support/documentation/8.2/doc/mop/dictionary.html#class-prototype
>>>
>>> Generic Function class-prototype class
>>>
>>> Returns a prototype instance of class. Whether the instance is
>>> initialized is not specified. The results are undefined if a portable
>>> program modifies the binding of any slot of prototype instance.
>>>
>>> This generic function signals an error if class has not been finalized.
>>>
>>> _______________________________________________
>>> armedbear-devel mailing list
>>> armedbear-devel at common-lisp.net
>>> http://common-lisp.net/cgi-bin/mailman/listinfo/armedbear-devel
>>>
>>
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>>
>