Re: [RFC]: replace-region-contents

[Marcin Borkowski <mbork@mbork.pl>]

On 2019-02-01, at 22:20, Tassilo Horn <tsdh@gnu.org> wrote:

> Hi all,
>
> on gnu-emacs-help I've asked why my wrapper command around
> `json-pretty-print' doesn't restore point although it uses
> `save-excursion'.  The reason is that `json-pretty-print' replaces the
> region with copy, delete, and insert.  Robert and Eli pointed me to the
> new `replace-buffer-contents' which allowed me to rewrite
> `json-pretty-print' in a way where point stays where it has been before
> pretty-printing:
>
> [...]
>
> --8<---------------cut here---------------start------------->8---
> ;; in subr-x.el (or wherever you please)
> (defun replace-region-contents (beg end extract-fn inject-fn)
>   "Replace the region between BEG and END using EXTRACT-FN and INJECT-FN.
>
> The current buffer is narrowed to the region between BEG and END,
> then EXTRACT-FN is called in order to extract some value.
> Thereafter, INJECT-FN is called with that value in a temporary
> buffer which it should populate.
>
> Finally, the region in the source buffer is replaced with the
> contents of the temporary buffer prepared by INJECT-FN using
> `replace-buffer-contents'."

It looks fairly interesting, and I can see quite a few uses for
a function like this.  The docstring doesn't seem to explain a lot to
me, though.  In particular, what are the arguments and return values of
EXTRACT-FN and INJECT-FN?

(I don't have time now to study the code.)

Best,

-- 
Marcin Borkowski
http://mbork.pl