Every developer is sometimes in the following situation - you’re inside the definition of something like a class or method, but the name of the class or method is not currently into view, but you’d very much like to know/see it. You can obviously scroll up and see what you need to, but there’s a simpler way to see the name you’re looking for - the built-in mode which-function-mode.

When which-function-mode is active you’ll see in the center of your modeline the name of the definition your cursor is currently in. Here’s the mode in action:

which-func modeline

And here’s how to enable it:


That way which-function-mode will be active in all major modes that support it. If you want to enable it only in specific modes you can do so like this:

(add-to-list 'which-func-modes 'ruby-mode)
(add-to-list 'which-func-modes 'emacs-lisp-mode)

By default ??? will be displayed when which-function-mode cannot determine the name (perhaps because you’re not actually in a definition or due to implementation limitations). You can change this to something else like this:

(setq which-func-unknown "n/a")

And what if you don’t like to have the definition name displayed in the mode-line? There’s a solution for you as well (suggested by Sebastian Wiesner). Use the following bit of code:

;; Show the current function name in the header line
(setq-default header-line-format
              '((which-func-mode ("" which-func-format " "))))
(setq mode-line-misc-info
            ;; We remove Which Function Mode from the mode line, because it's mostly
            ;; invisible here anyway.
            (assq-delete-all 'which-func-mode mode-line-misc-info))

And you’ll get the following result:

which-func header

That’s all for today, folks! Hack Emacs Lisp & prosper!