Switching between Header and Implementation Files with Emacs

I often find myself working with C or C++ code that follows the pattern of parallel source/include directories, probably with lots of layers in between (e.g. project/include/some-controller/some-aspect/something.h and project/src/some-controller/some-aspect/something.cpp). Quickly switching between both saves on keystrokes and sanity, so I wrote this little chunk of elisp, bound to ctrl-alt-g (for no particular reason other than the combination is easy to mash):

(defun djw-c-toggle-impl-header-view (create-if-nonexistent)
  (interactive "P")
  (let* ((mode (if (string-equal (file-name-extension (buffer-file-name))
     "h")
     :switch-to-implementation :switch-to-header))
  (toggle-tags (list (cons "/Include/" "/Src/")
       (cons "/include/" "/src/")))
  (from-fn (if (eq mode :switch-to-implementation)
        #'car #'cdr))
  (to-fn (if (eq mode :switch-to-implementation)
      #'cdr #'car))
  (source-file-name (buffer-file-name))
  (case-fold-search nil)) ;; I want case-sensitive matching throughout this block.
    (dolist (pair toggle-tags)
      (setf source-file-name (replace-regexp-in-string (funcall from-fn pair)
             (funcall to-fn pair)
             source-file-name)))
    (setf source-file-name
   (replace-regexp-in-string
    (if (eq mode :switch-to-implementation)
        "h\$" "cpp\$")
    (if (eq mode :switch-to-implementation)
        "cpp" "h")
    source-file-name))
    (message (format "Looking for %s" source-file-name))
    (if (or (file-exists-p source-file-name)
     create-if-nonexistent)
 (find-file source-file-name)
 (message (format "Can't find '%s'" source-file-name)))))

If the counterpart file is missing, it won't be created unless the function is invoked with a prefix argument (C-u C-M-g).

There's probably some extension to CC mode or the like that already does something like this, but in the absence of reading the manual, this works well for me.