Add a function to easily swap strings in a file

lisp/text-manip.el

@@ -49,6 +49,28 @@ DELIMITED, START, and END are passed down verbatim to `perform-replace'."
                                 ,from-string))
    t t delimited nil nil start end))
 
+;; From https://emacs.stackexchange.com/a/27170/507
+(defun query-swap-strings (from-string to-string &optional delimited start end)
+  "Swap occurrences of FROM-STRING and TO-STRING.
+
+DELIMITED, START, and END are passed to `replace-eval-replacement' verbatim."
+  (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))
+
 (provide 'text-manip)
 
 ;;; text-manip.el ends here