Re: meta information about structure types

[Sam S. <sd...@gn...>]

> * Bruno Haible <oe...@py...t> [2005-01-25 20:24:47 +0100]:
>
>> (let ((c (find-class name)))
>>   (if c
>>       (class-direct-slots c)
>>       (structure-direct-slots name)))
>
> This is a hypothetical use case. Doesn't occur in practice. (Where
> would the 'name' come from?)

I save my objects in text files, writing type and slot names and values.
Sometimes I use DEFCLASS and sometimes DEFSTRUCT.
I don't want to have to regenerate all my data if I decide to convert my
structs to classes.

>> (let ((c (class-of object)))
>>   (if (class-p c)
>>       (class-direct-slots c)
>>       (structure-direct-slots (class-name c))))
>
> Yes. The second branch can never be taken. For a good reason: There's
> no way to use the structure-* API when all you have is an object.  If
> an object is given and it might be a list or a vector, you cannot
> determine which structure it comes from. (Is #(FOO 3 BAR #\X BAZ) a
> FOO, a BAR, or a BAZ?) Therefore when all you have is an object, you
> can only rely on the class-* API.

will this work:
(defstruct foo a b c)
(class-direct-slots (find-class 'foo))


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