A use-package declaration for simplifying your .emacs
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The use-package declaration macro allows you to isolate package configuration in your ".emacs" in a way that is performance-oriented and, well, just tidy. I created it because I have over 80 packages that I use in Emacs, and things were getting difficult to manage. Yet with this utility my total load time is just under 1 second, with no loss of functionality!

Here is the simplest use-package declaration:

(use-package foo)

This loads in the package foo, but only if foo is available on your system. If not, a warning is logged to your *Messages* buffer. If it succeeds, a message about "Loading foo" is logged -- along with the time it took to load if that time is over 0.01s.

Use the :init keywoard to do some stuff to initialize foo, but only if foo actually gets loaded:

(use-package foo
    (setq foo-variable t)
    (foo-mode 1)))

A very common thing to do when loading a module is to bind a key to primary commands within that module:

(use-package ace-jump-mode
  :bind ("C-." . ace-jump-mode))

This does two things: first, it creates autoload for the ace-jump-mode command, and defers loading of ace-jump-mode until you actually use it. Second, it binds the key C-. to that command. After loading, you can use M-x describe-personal-keybindings to see all such bindings you've set throughout your Emacs.

A more literal way to do the exact same thing is:

(use-package ace-jump-mode
  :commands ace-jump-mode
  (bind-key "C-." 'ace-jump-mode))

When you use the :commands keyword, it creates autoloads for those commands and defers loading of the module until they are used. In this case, the :init form is always run -- even if ace-jump-mode might not be on your system. So remember to keep :init activities to only those that would succeed either way.

Similar to :bind, you can use :mode and :interpreter to establish a deferred binding within auto-mode-alist and auto-interpreter-alist. The specifier to either keyword can be a single cons or a list:

(use-package python-mode
  :mode ("\\.py$" . python-mode)
  :interpreter ("python" . python-mode))

If you aren't using :commands, :bind, :mode, or :interpreter (all of which imply :commands), you can still defer loading with the :defer keyword:

(use-package ace-jump-mode
  :defer t
    (autoload 'ace-jump-mode "ace-jump-mode" nil t)
    (bind-key "C-." 'ace-jump-mode)))

This does exactly the same thing as the other two commands above.

A companion to the :init keyword is :config. Although :init always happens in the case of deferred modules (which are likely to be the most common kind), :config form only run after the module has been loaded by Emacs:

(use-package ace-jump-mode
  :bind ("C-." . ace-jump-mode)
  (message "Yay, ace-jump-mode was actually loaded!"))

You will see a "Configured..." message in your *Messages* log when a package is configured, and a timing if the configuration time was longer than 0.01s. You should keep :init forms as simple as possible, and put as much as you can get away with on the :config side.

You can have both :init and :config:

(use-package haskell-mode
  :commands haskell-mode
  (add-to-list 'auto-mode-alist '("\\.l?hs$" . haskell-mode))
    (use-package inf-haskell)
    (use-package hs-lint)))

In this case, I want to autoload the command haskell-mode from "haskell-mode.el", add it to auto-mode-alist at the time ".emacs" is loaded, but wait until after I've opened a Haskell file before loading "inf-haskell.el" and "hs-lint.el".

The :bind keyword takes either a cons or a list of conses:

(use-package hi-lock
  :bind (("M-o l" . highlight-lines-matching-regexp)
         ("M-o r" . highlight-regexp)
         ("M-o w" . highlight-phrase)))

The :commands keyword likewise takes either a symbol or a list of symbols.

You can use the :if keyword to predicate the loading and initialization of a module. For example, I only want an edit-server running for my main, graphical Emacs, not for Emacsen I may start at the command line:

(use-package edit-server
  :if window-system
    (add-hook 'after-init-hook 'server-start t)
    (add-hook 'after-init-hook 'edit-server-start t)))

The :disabled keyword can be used to turn off a module that you're having difficulties with, or to stop loading something you're not really using at the present time:

(use-package ess-site
  :disabled t
  :commands R)

Another feature of use-package is that it always loads every file that it can when your ".emacs" is being byte-compiled (if you do that, which I recommend). This helps to silence spurious warnings about unknown variables and functions.

However, there are times when this is just not enough. For those times, use the :defines keyword to introduce empty variable definitions solely for the sake of the byte-compiler:

(use-package texinfo
  :defines texinfo-section-list
  :commands texinfo-mode
  (add-to-list 'auto-mode-alist '("\\.texi$" . texinfo-mode)))

If you need to silence a missing function warning, do it with an autoload stub in your :init block:

(use-package w3m
  :commands (w3m-browse-url w3m-session-crash-recovery-remove)
    (autoload 'w3m-search-escape-query-string "w3m-search")))

If your package needs a directory added to the load-path in order load, use :load-path. It takes a string or a list of strings. If the path is relative, it will be expanded within user-emacs-directory:

(use-package ess-site
  :disabled t
  :load-path "site-lisp/ess/lisp/"
  :commands R)

Lastly, use-package provides built-in support for the diminish utility, if you have that installed. It's purpose is to remove strings from your mode-line that would otherwise always be there and provide no useful information. It is invoked with the :diminish keyword, which is passed the minor mode symbol:

(use-package abbrev
  :diminish abbrev-mode
  (if (file-exists-p abbrev-file-name)

  (add-hook 'expand-load-hook
            (lambda ()
              (add-hook 'expand-expand-hook 'indent-according-to-mode)
              (add-hook 'expand-jump-hook 'indent-according-to-mode))))

If you noticed that this declaration has neither a :bind, :commands or :defer keyword: congratulations, you're an A student! What it means is that both the :init and :config forms will be executed when ".emacs" is loaded, with no delays until later. Is this useful? Not really. I just happen to like separating my configuration into things that must happen at startup time, and things that could potentioally wait until after the actual load. In this case, everything could be put inside :init and there would be no difference.

For el-get users

You can use use-package as a way to create source definitions for el-get. All that's needed is to add a :type keyword to your declaration. When this is present, certain keywords get translated to what el-get expects in the el-get-sources list:

:config   -> :after
:requires -> :depends

A :name will be added also, if one is not provided explicitly, which will be the same as the name of the package.

But why would you want to use use-package when you have el-get? My answer is that I'd like to use el-get to install and update some packages, but I don't want it managing configuration. Just loading el-get -- without call (el-get 'sync') -- takes a quarter second on my machine. That's 25% of my load time!use-package` is designed for performance, so I only want to load el-get when it's time to install or update on of my used packages.

Here is the use-package declaration I use for setting up el-get, but only when I want to install or update:

(defvar el-get-sources nil)

(use-package el-get
  :commands (el-get
  (defun el-get-read-status-file ()
    (mapcar #'(lambda (entry)
                (cons (plist-get entry :symbol)
                      `(status "installed" recipe ,entry)))