Re: [RFC]: replace-region-contents

[Tassilo Horn <tsdh@gnu.org>]

Marcin Borkowski <mbork@mbork.pl> writes:

>>>> --8<---------------cut here---------------start------------->8---
>>>> (defun replace-region-contents (beg end replace-fn)
>>>>   (save-excursion
>>>>     (save-restriction
>>>>       (narrow-to-region beg end)
>>>>       (goto-char (point-min))
>>>>       (let ((repl (funcall replace-fn)))
>>>> 	(if (bufferp repl)
>>>> 	    (replace-buffer-contents repl)
>>>> 	  (let ((source-buffer (current-buffer)))
>>>> 	    (with-temp-buffer
>>>> 	      (insert repl)
>>>> 	      (let ((tmp-buffer (current-buffer)))
>>>> 		(set-buffer source-buffer)
>>>> 		(replace-buffer-contents tmp-buffer)))))))))
>>>> --8<---------------cut here---------------end--------------->8---
>>>
>>> LGTM
>>
>> How would I actually use that version with a replace-fn returning a
>> buffer and not a string?  It looks to me that I need to do the whole
>> ceremony of creating a temporary buffer, setting buffers, and ensuring
>> that the temporary buffer is killed even in the case of an abnormal exit
>> myself.  That's the hassle my original version tried to eliminate in the
>> first place...
>
> I did not follow the whole thread, but why wouldn't `with-temp-buffer'
> be a suitable candidate to conduct exactly the ceremony you mentioned?

You cannot use `with-temp-buffer' inside replace-fn and then return that
temp buffer, because it'll be killed as soon as control flow escapes it.
So you need to define your replace-fn in the lexical scope of an already
established `with-temp-buffer' form.  But since you will need to access
the source buffer, you need to manually arrange in which buffer to
operate what.

> Also, at least sometimes, buffers are better than strings to perform
> e.g. replacements.

Yes, sure, although replacements could be performed in the source buffer
itself.

Bye,
Tassilo