Proposal: prefer #' (sharp quote) when quoting function names

[skeeto]

When quoting symbols to access their function definitions, prefer the use of sharp quotes. This allows the bytecompiler to check if the function exists, issuing a warning just like it would when calling an undefined function.

This would change the anonymous function example.

(cl-remove-if-not #'evenp numbers)

Sharp quoting has become a lot more relevant with the introduction of lexical scoping.

(defun foo ()
  :global)

(cl-flet ((foo () :local))
  (list (funcall 'foo) (funcall #'foo)))
;; => (:global :local)

[Malabarba]

I was just about to recommend this as well. Emacs source does this AFAIK.

[bbatsov]

Agreed. Would you submit a PR Rregarding this?

On Thursday, September 4, 2014, Artur Malabarba notifications@github.com wrote:

I was just about to recommend this as well. Emacs source does this AFAIK.

— Reply to this email directly or view it on GitHub https://github.com/bbatsov/emacs-lisp-style-guide/issues/7#issuecomment-54543062 .

[shosti]

I'm not entirely sure about this--most examples from the manual don't sharp-quote (the Emacs source code seems pretty mixed). I think literally the only case where it makes a difference is cl-flet, and that has nothing to do with lexical scoping (it behaves the same with lexical scoping disabled). I guess there's no harm in it, but I'm just not sure it's important enough to be a hard recommendation.

[skeeto]

@bbatsov Sure thing!

@shosti The manual doesn't say sharp quoting is the same. It says it's syntax for function. It has a similar result but with subtle, important differences. When the manual is referring to global functions for key bindings (global-set-key, define-key) it uses a plain quote, which is reasonable. Otherwise the examples use sharp quote. Here's another example of where it's different than quoting. If this is the content of a file tmp.el:

(funcall #'foo)

When I byte compile it I get this:

tmp.el:3:1:Warning: the function `foo' is not known to be defined.

Change it to this and the warning goes away:

(defun foo ())
(funcall #'foo)

The sharp quote allowed the compiler to check my work for mistakes.

[shosti]

OK, that's convincing (I was mixing it up with the part in the manual about sharp-quoted lambda expressions, which are equivalent to non-quoted lambda expressions).