Re: looking-at-p slower than looking-at

[Marcin Borkowski <mbork@mbork.pl>]

On 2015-11-25, at 14:58, Nicolas Richard <nrichard@ulb.ac.be> wrote:

> Marcin Borkowski <mbork@mbork.pl> writes:
>
>> You might also (depending on your use-case) want to use looking-at-p,
>> which is marginally slower than looking-at, but does not modify match
>> data.
>
> Why is it slower and how much slower is it ? I don't see how it can
> happen from its implementation:
>
> (defsubst looking-at-p (regexp)
>   "\
> Same as `looking-at' except this function does not change the match data."
>   (let ((inhibit-changing-match-data t))
>     (looking-at regexp)))

One more function call and one more variable binding.  IMHO it /must/ be
slower, though I think the effect is negligible.

OTOH, this trivial and unscientific test:

(setq foo "foo")
(benchmark 10000000 (looking-at foo))
(benchmark 10000000 (looking-at-p foo))

was not conclusive.  (AFAIU, it is of utmost importance that you don't
use literal strings in such a test, since then it is much more probable
that GC will kick in.  Am I right?)

> thanks,

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University