Add function so/query-swap-strings

lisp/text-manip.el

@@ -15,3 +15,28 @@
                  (list (if current-prefix-arg 'unfill) t)))
   (let ((fill-column (if unfill (point-max) fill-column)))
     (fill-paragraph nil region)))
+
+;; Copied from http://emacs.stackexchange.com/a/27170/507
+(defun so/query-swap-strings (from-string
+                              to-string
+                              &optional delimited start end)
+  "Swap occurrences of FROM-STRING and TO-STRING."
+  (interactive
+   (let ((common
+          (query-replace-read-args
+           (concat "Query swap"
+                   (if current-prefix-arg
+                       (if (eq current-prefix-arg '-) " backward" " word")
+                     "")
+                   (if (use-region-p) " in region" ""))
+           nil)))
+     (list (nth 0 common) (nth 1 common) (nth 2 common)
+           (if (use-region-p) (region-beginning))
+           (if (use-region-p) (region-end)))))
+  (perform-replace
+   (concat "\\(" (regexp-quote from-string) "\\)\\|" (regexp-quote to-string))
+   `(replace-eval-replacement replace-quote
+                              (if (match-string 1)
+                                  ,to-string
+                                ,from-string))
+   t t delimited nil nil start end))