Re: `looking-back' strange warning

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

Am 03.10.2015 um 08:26 schrieb Tassilo Horn:
> Drew Adams <drew.adams@oracle.com> writes:
>
>>> This version is about 6 times faster in the t case and a still a bit
>>> faster in the nil case where the char before point is already different
>>> (which is the best case for your function).
>>>
>>> (defun chars-before (chars)
>>>    "Return non-nil if the literal string CHARS is right before point.
>>> This is more efficient that `looking-back' for this use case."
>>>    (let ((beg (- (point) (length chars))))
>>>      (unless (< beg 0)
>>>        (save-excursion
>>> 	  (goto-char beg)
>>> 	  (looking-at (regexp-quote chars))))))
>> OK.  Good to know.
>>
>> See also bug #17284,
>> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17284,
>> where this has been discussed and I and others proposed
>> code for this.
> Martin's version is faster than mine, so no need to propose it.
>
>> You are welcome to contribute to that (short) bug thread,
>> or to otherwise try to get such a function added to Emacs.
> I think that function is not really a viable drop-in replacement for
> typical `looking-back' calls.  The latter is most frequently used to
> decide "am I behind some word or sequence of words, and I don't care
> about whitespace?".
>
> Bye,
> Tassilo
>

Just for fun:

(defun looking-back-string (string)
   "Return non-nil if the literal STRING is right before point.
This is more efficient that `looking-back' for this use case."
   (string= string (ignore-errors (buffer-substring-no-properties (- 
(point) (length string)) (point)))))