* What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on?
@ 2014-07-27 3:32 Dmitry Gutov
2014-07-27 8:16 ` Stefan Monnier
0 siblings, 1 reply; 4+ messages in thread
From: Dmitry Gutov @ 2014-07-27 3:32 UTC (permalink / raw)
To: help-gnu-emacs
[-- Attachment #1: Type: text/plain, Size: 771 bytes --]
1. Save a.el and b.el to the same dir.
2. Open b.el, type M-x eval-buffer.
3. Evaluate (b-foo), see 4 in the echo area.
Note that the assertion in `b-bar' succeeds, and so while `a-a' is not
globally bound, it's visible from `b-bar'.
If I replace the definition of b-bar with
```
(defvar a-a)
(defun b-bar ()
(cl-assert (= a-a 4))
(let ((a-a 5))
(a-bar)))
```
or even with
```
(defun b-bar ()
(defvar a-a)
(cl-assert (= a-a 4))
(let ((a-a 5))
(a-bar)))
```
(which apparently doesn't make `a-a' globally defined in that file, ref.
http://debbugs.gnu.org/18059)
then, as I'd expect, after M-x eval-buffer, (b-bar) evaluates to 5.
Why does this happen? Is (defvar foo) the recommended option to use with
lexical-binding on?
-- Dmitry
[-- Attachment #2: a.el --]
[-- Type: text/x-emacs-lisp, Size: 118 bytes --]
(defvar a-a)
(defun a-foo (callback)
(let ((a-a 4))
(funcall callback)))
(defun a-bar ()
a-a)
(provide 'a)
[-- Attachment #3: b.el --]
[-- Type: text/x-emacs-lisp, Size: 222 bytes --]
;;; -*- lexical-binding: t -*-
(let ((load-path '(".")))
(require 'a))
(defun b-foo ()
(a-foo #'b-bar))
(defun b-bar ()
(declare (special a-a))
(cl-assert (= a-a 4))
(let ((a-a 5))
(a-bar)))
(provide 'b)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on?
2014-07-27 3:32 What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on? Dmitry Gutov
@ 2014-07-27 8:16 ` Stefan Monnier
2014-07-27 9:00 ` Dmitry
0 siblings, 1 reply; 4+ messages in thread
From: Stefan Monnier @ 2014-07-27 8:16 UTC (permalink / raw)
To: help-gnu-emacs
(declare (special foo))
is a hack defined in CL. It predates lexical-binding and I don't
think anyone has tried to adapt it to lexical-binding, so I don't know
what it does in the case of lexical-binding.
Stefan
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on?
2014-07-27 8:16 ` Stefan Monnier
@ 2014-07-27 9:00 ` Dmitry
2014-07-27 9:58 ` Stefan Monnier
0 siblings, 1 reply; 4+ messages in thread
From: Dmitry @ 2014-07-27 9:00 UTC (permalink / raw)
To: Stefan Monnier; +Cc: help-gnu-emacs
Stefan Monnier <monnier@iro.umontreal.ca> writes:
> (declare (special foo))
>
> is a hack defined in CL. It predates lexical-binding and I don't
> think anyone has tried to adapt it to lexical-binding, so I don't know
> what it does in the case of lexical-binding.
Thanks! So, you would advise not to use it in lexical-binding code at
all?
I think the biggest problem with it is it sorta-works-but-not-exactly.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on?
2014-07-27 9:00 ` Dmitry
@ 2014-07-27 9:58 ` Stefan Monnier
0 siblings, 0 replies; 4+ messages in thread
From: Stefan Monnier @ 2014-07-27 9:58 UTC (permalink / raw)
To: help-gnu-emacs
> Thanks! So, you would advise not to use it in lexical-binding code at all?
I think so, yes.
Stefan
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2014-07-27 9:58 UTC | newest]
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2014-07-27 3:32 What's the difference between (defvar foo) and (declare (special foo)), with lexical-binding on? Dmitry Gutov
2014-07-27 8:16 ` Stefan Monnier
2014-07-27 9:00 ` Dmitry
2014-07-27 9:58 ` Stefan Monnier
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