equality predicate option for `next-single-property-change'?

[Joe Corneli]

It seems like `next-single-property-change' and other
functions for text property search should take an optional
predicate to be used in the test.  For example, instead of
testing

         && EQ (here_val, textget (next->plist, prop))

in line 1056 of textprop.c, the user-supplied predicate
would be used for comparison instead.

I can write Elisp functions that will achieve the same effect,
but I don't know if it is as fast as it would be in C.

(defun next-single-property-change--predicate
  (pos prop &optional test)
  (let ((starting (get-text-property pos prop))
        (index pos)
        (cmpfct (or test
                    'eq)))
    (save-excursion 
      (while (and (setq index (1+ index))
                  (< index (point-max))
                  (funcall cmpfct
                           starting 
                           (get-text-property index prop)))))
    (when (< index (point-max))
      index)))


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<up> <up> <down> <down> <down> <down> <down> <down> 
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