Re: Retrieve front-advance from make-overlay

[David Kastrup]

"Lennart Borgman (gmail)" <address@hidden> writes:

> David Kastrup wrote:
>> "Lennart Borgman (gmail)" <address@hidden> writes:
>>
>>> Stefan Monnier wrote:
>>>>> Is it possible to retrieve from an overlay the parameters front-advance 
>>>>> and
>>>>> rear-advance that was given to make-overlay?
>>>>> Without that it is not possible to make a new copy of an overlay AFAICS.
>>>> The source code of `copy-overlay' answers this question.
>>> Thanks. Indeed it does ;-)  -- BTW copy-overlay is not mentioned in Info.
>>
>> (defun overlay-polarities (ov)
>>   (let ((buf (overlay-buffer ov))
>>         (start (overlay-start ov))
>>         (end (overlay-end ov)))
>>      (unwind-protect
>>         (with-temp-buffer
>>            (move-overlay ov 1 1)
>>            (insert " ")
>>            (list (> (overlay-start ov) 1)
>>                  (> (overlay-end ov) 1)))
>>        (move-overlay ov buf start end))))
>>
>> This at least has the advantage of not touching the original buffer.
>> But it is tasteless nevertheless.
>
>
> Thanks David, I did not that one. I will try it.

It was untested, and naturally, it is wrong.  Both calls to
move-overlay.  You have to use

(move-overlay ov 1 1 (current-buffer))

and

(move-overlay ov start end buf)

instead, respectively.  There are probably more errors: I still did
not test it.

It is basically just a sketch, but should be close to working.

-- 
David Kastrup