dot-emacs-snippet-read-only-toggle

;; The variable ‘emacs-major-verseion’ and the variable ‘emacs-minor-version’
;; both first existed in GNU Emacs 19.23.
;;
;; Since GNU Emacs 24.3, the function ‘toggle-read-only’ is obsolete; the
;; recommendation is to use the function ‘read-only-mode’ instead. Note that
;; ‘read-only-mode’ is, by default, set to "C-x C-q", but I’ve got 20+ years
;; of muscle memory in my hands that want to use "C-c r" to toggle the
;; "read-onlyness" of the buffer.
;;
;; See also the function ‘view-mode’ and the variable ‘view-read-only’; having
;; the latter set non-nil means buffers visiting files read-only do so in View
;; mode (note that its default value is nil). It also controls whether
;; ‘read-only-mode’ will enable view mode for buffers that you flag as
;; read-only by running ‘read-only-mode’ while visiting them.
;;
;; FIXME: Decide whether View mode is something we want to get used to. For
;;        now, I’m leaving ‘view-read-only’ with its default value of nil,
;;        which preserves the historical behavior.
;;
;(global-set-key [?\C-c ?r] 'toggle-read-only)
(if (not (boundp 'emacs-major-version))
    (display-warning '(:ads-dot-emacs) (format ".emacs: symbol ‘emacs-major-version’ not bound; omitting read-only keybinding"))
  
  (if (not (boundp 'emacs-minor-version))
      (display-warning '(:ads-dot-emacs) (format ".emacs: symbol ‘emacs-minor-version’ not bound; omitting read-only keybinding"))

    (let ((wanted-fn-symbol (if (or (and (=  emacs-major-version 24)
                                         (>= emacs-minor-version  3))
                                    (> emacs-major-version 24))
                                'read-only-mode    ; GNU Emacs >= 24.3
                              'toggle-read-only))) ; GNU Emacs <  24.3

      (global-set-key [?\C-c ?r] wanted-fn-symbol))))