bug#26338: 26.0.50; Collect all matches for REGEXP in current buffer

[Tino Calancha <tino.calancha@gmail.com>]

On Sun, 2 Apr 2017, Dmitry Gutov wrote:

> On 02.04.2017 15:41, Tino Calancha wrote:
>
>> we have `count-matches' in replace.el, which returns the
>> number of matches of a regexp.  Why not to have an standard
>> function `collect-matches' as well?
>> 
>> I know `xref-collect-matches' but it uses grep program: some users might
>> not have grep installed, or they may prefer to use Emacs regexps.
>> 
>> I've being using for a while something similar than the patch below.
>> Probably it doesn't need to be a command, just a normal function.
>> 
>> What do you think?
> When used interactively, isn't M-x occur doing something like this?
>
> And for Elisp programs, (while (re-search-forward ...)) is usually 
> sufficient. That's a three-liner at worst.
It might be argue the same for occur.  You can just increase a counter
inside (while (re-search-forward ...))

> And I've never had a need to limit the number of matches, personally.
I did often while implementing Bug#25493.  Let's say i am interested in
the last 200 commits modifying a file foo.el.
M-x: find-library foo RET
C-x v l
M-: (setq hashes (collect-matches "^commit \\([[:xdigit:]]+\\)" nil 1 200))

In this case, there is no need to go beyond 200 that's why the limit 
argument might be useful.

Another example,
let's say i want to know the two first defun's in subr.el
M-x: find-library subr RET
M-: (collect-matches "^(defun \\([^[:blank:]]+\\)" nil 1 2) RET

Of course you could do:
M-: (seq-take (collect-matches "^(defun \\([^[:blank:]]+\\)" nil 1) 2) RET
;; But if you just want the 2 leading defun's this is a waste.