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Re: How to determine buffer change


From: Thorsten Jolitz
Subject: Re: How to determine buffer change
Date: Sat, 05 Apr 2014 15:23:22 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Thorsten Jolitz <address@hidden> writes:

> Eli Zaretskii <address@hidden> writes:
>
>>> From: Thorsten Jolitz <address@hidden>
>>> Date: Sat, 05 Apr 2014 13:41:41 +0200
>>> 
>>> in a program I insert text in an empty temporary edit-buffer, what of
>>> course modifies the `buffer-undo-list'.
>>> Assume that at this moment (lets call it time T1)
>>> 
>>> ,------------------------------
>>> | M-: (length buffer-undo-list)
>>> `------------------------------
>>> 
>>> returns 9. 
>>> 
>>> Now when there are changes to the text in the edit-buffer, these are
>>> copied to the original buffer after quitting. But when nothing has
>>> changed after the insertion of the original text, it would be better to
>>> simply discard the edit-buffer and not touch the original buffer at
>>> all. 
>>> 
>>> I could remember the length of the buffer-undo-list at time T1 and then
>>> check if it changed when quitting, but this does not seem very robust,
>>> since this length grows and shrinks in both directions.
>>
>> Did you try using buffer-modified-tick?
>
> Thats it probably, thanks.
>
> Still have to figure out when to store the ticks - although I think I
> set them directly after edit-buffer setup and directly before
> edit-buffer quitting, the tick values differ quite a lot although no
> editing took place, e.g.:
>
> ,---------------------
> | tick1: 48 tick2: 97
> | tick1: 76 tick2: 229
> `---------------------

Actually I have this as last expression in the edit-buffer set-up
function: 

#+begin_src emacs-lisp
  (defun tj/setup-edit-buffer ()
    ;; [...]
    ;; store buffer-modified-tick at time T1
    (setq edit-buffer-modified-tick-1
          (buffer-modified-tick)))
#+end_src

and this as first expression in the edit-buffer quit function:

#+begin_src emacs-lisp
    (defun tj/quit-edit-buffer ()
    ;; store buffer-modified-tick at time T2
    (setq edit-buffer-modified-tick-2 (buffer-modified-tick))
    (if (eq edit-buffer-modified-tick-1
            edit-buffer-modified-tick-2)
        (progn
          ;; [...]
          )))
#+end_src

and I did nothing else but calling and quitting the edit-buffer,
however ticks have almost doubled in numbers in between:

,--------------------
| tick1: 48 tick2: 97
`--------------------

Can that be related to buffer fontifying or other stuff that happens
lazily with a bit lag to the initial buffer set-up?

-- 
cheers,
Thorsten




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