Replacing buffer contents --- without disturbing markers

Replacing buffer contents --- without disturbing markers

[Daniel Colascione]

For a mode I'm writing, I have to temporarily replace certain parts of
the buffer with placeholder text. I'm using this function to do it:

(defun ntcmd-inplace-replace (replacement)
  "Replace the characters at point with REPLACEMENT without disturbing markers.

Leave point after replacement. The number of characters replaced
is the length of REPLACEMENT."

  (loop for c across replacement
        ;; Replace the character after point with the next character
        ;; from replacement. We must worry about two kinds
        ;; of marker: those pointing at point (including (point)), and
        ;; those pointing at (1+ (point)).
        ;;
        ;; Mentally run through the code below, and you'll see that
        ;; both kinds of marker are preserved.
        ;;
        do (progn
             (forward-char 1)
             (insert-before-markers c)
             (backward-char 1)
             (delete-char -1)
             (forward-char 1))))

Is it possible to do better? replace-match squashes markers.

Re: Replacing buffer contents --- without disturbing markers

[David Kastrup]

Daniel Colascione <dan.colascione@gmail.com> writes:

> For a mode I'm writing, I have to temporarily replace certain parts of
> the buffer with placeholder text. I'm using this function to do it:
>
> (defun ntcmd-inplace-replace (replacement)
>   "Replace the characters at point with REPLACEMENT without disturbing markers.
>
> Leave point after replacement. The number of characters replaced
> is the length of REPLACEMENT."
>
>   (loop for c across replacement
>         ;; Replace the character after point with the next character
>         ;; from replacement. We must worry about two kinds
>         ;; of marker: those pointing at point (including (point)), and
>         ;; those pointing at (1+ (point)).
>         ;;
>         ;; Mentally run through the code below, and you'll see that
>         ;; both kinds of marker are preserved.
>         ;;
>         do (progn
>              (forward-char 1)
>              (insert-before-markers c)
>              (backward-char 1)
>              (delete-char -1)
>              (forward-char 1))))
>
> Is it possible to do better? replace-match squashes markers.

Not sure whether make-indirect-buffer would keep the markers in piece.

-- 
David Kastrup

Re: Replacing buffer contents --- without disturbing markers

[Stefan Monnier]

>         ;; Replace the character after point with the next character
>         ;; from replacement. We must worry about two kinds
>         ;; of marker: those pointing at point (including (point)), and
>         ;; those pointing at (1+ (point)).

Actually there 4 kinds: at point, at point+1, multiplied by the two
insertion-types.  Your code works with the default insertion-type, but
not the other (don't worry: I don't think you can do much better).


        Stefan

Re: Replacing buffer contents --- without disturbing markers

[Richard Stallman]

    For a mode I'm writing, I have to temporarily replace certain parts of
    the buffer with placeholder text. I'm using this function to do it:

In general, temporarily replacing text has some drawbacks.
If you can find a way to do the overall job without that method,'
it is likely to be better.