Re: [Emacs-diffs] trunk r116995: cl-lib defstruct introspection

[Daniel Colascione <dancol@dancol.org>]

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On 04/21/2014 07:03 PM, Stefan Monnier wrote:
>> Can it? I tried it in vc-dir and got a completely unrelated ChangeLog hunk.
> 
> Yes, there's a long-standing problem in vc-dir, such that it only works
> well if you mark the files you're going to commit (basically the
> changelog-copying feature needs the list of files that will be committed
> and vc-dir doesn't provide it unless you manually mark each file).
> 
> Patch welcome.
> 
>>>>> I'm curious: when/where did you bump against a need for that?
>>>> I have a few private macros that lexically bind structure slots,
>>> Which part makes it impossible/impractical to use standard accessors for
>>> that?
>> :conc-name, for starters. Also, :read-only, although you could argue
>> that you shouldn't go around mutating read-only slots anyway.
> 
> I guess I don't know what you mean by "lexically bind structure slots".
> Can you give an example?

Something like this. (This is the private code I was talking about, so
it doesn't use the sames in the checked-in patch.)

(defmacro* jez-with-slots (spec-list (type inst) &body body)
  "Like `with-slots', but for structs."
  (if (symbolp inst)
      `(symbol-macrolet
           ,(loop for spec in spec-list
                  collect `(,spec (jez-slot-value ',type ,inst ',spec)))
         ,@body)
    (let ((inst-symbol (gensym "with-struct-slots")))
      `(let ((,inst-symbol ,inst))
         (jez-with-slots
             ,spec-list ,inst-symbol ,@body)))))


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