Re: `looking-back' strange warning

[Andreas Röhler]

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)))))