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with-current-buffer mystery
From: |
Ryan Yeske |
Subject: |
with-current-buffer mystery |
Date: |
Thu, 25 Nov 2004 07:57:28 GMT |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50 |
Hello,
I'm writing some code that appends text from a process into a buffer.
I copied the filter code from the info node (elisp)Filter Functions:
(defun ordinary-insertion-filter (proc string)
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))))
The text below this code fragment says:
The reason to use `with-current-buffer', rather than using
`save-excursion' to save and restore the current buffer, is so
as to preserve the change in point made by the second call to
`goto-char'.
Right. So `with-current-buffer' should preserve the current buffer,
but allow changes to the point?
When I eval the following expressions, I found that it seems to depend
on whether or not the buffer is visible.
;; create a dummy buffer with text
(progn
(pop-to-buffer (get-buffer-create "*dummy*"))
(erase-buffer)
(insert "1\n2\n3\n")
(goto-char (point-min)))
Notice point is at the beginning of buffer. Eval the next
expression with *dummy* still visible in other-window.
;; goto end of buffer and insert a 4, note where point is
(with-current-buffer (get-buffer-create "*dummy*")
(goto-char (point-max))
(insert "4")
(newline))
The 4 is inserted at the correct position, but point did not
permanently change. Switch to that buffer and check.
(pop-to-buffer "*dummy*")
So, maybe I'm misunderstanding `with-current-buffer'.
If you repeat the second step, but with *dummy* buried:
(delete-other-windows)
(with-current-buffer "*dummy*"
(goto-char (point-max))
(insert "5")
(newline))
(pop-to-buffer "*dummy*")
The 5 is in the right place, and the point is at the end.
What is going on?
Any help or explanations would be greatly appreciated.
Ryan
- with-current-buffer mystery,
Ryan Yeske <=