From: Philipp Stephani <p.stephani2@gmail.com>
To: Yuan Fu <casouri@gmail.com>
Cc: help-gnu-emacs <help-gnu-emacs@gnu.org>
Subject: Re: Plist-put changes literal argument
Date: Sat, 5 Sep 2020 17:53:52 +0200 [thread overview]
Message-ID: <CAArVCkQkdLoTsdap1SOyzyLg6K_7icbb=QiPmfHPjx+zCJKVig@mail.gmail.com> (raw)
In-Reply-To: <F64BE28B-8AA0-46E4-8B69-7C5B1D3C67F1@gmail.com>
Am Do., 3. Sept. 2020 um 01:59 Uhr schrieb Yuan Fu <casouri@gmail.com>:
>
>
>
> > On Sep 2, 2020, at 7:55 PM, Yuan Fu <casouri@gmail.com> wrote:
> >
> > I found plist-put changes the literal argument I pass to a function:
> >
> > (defun test ()
> > (test-2 '(:a b)))
> >
> > (defun test-2 (form)
> > (print form)
> > (plist-put form :a 'c)
> > nil)
> >
> > (progn (test) (test))
> >
> > (:a b)
> >
> > (:a c)
> > nil
> >
> > I thought Elisp is pass-by-copy? Is this expected?
> >
> > P.S., (setf (alist-get )) does the same, I guess this IS expected?
> >
> > Yuan
>
> I also tried setcar, same result. So Elisp doesn’t copy arguments?
Lists (actually all values except fixnums/small integers) are always
passed by reference; or, in other words, a list argument actually
contains a pointer to the list, not the list itself. Copying the
pointer doesn't copy the list.
prev parent reply other threads:[~2020-09-05 15:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 23:55 Plist-put changes literal argument Yuan Fu
2020-09-02 23:59 ` Yuan Fu
2020-09-03 0:18 ` Yuan Fu
2020-09-03 0:53 ` Noam Postavsky
2020-09-05 15:55 ` Philipp Stephani
2020-09-06 15:23 ` Yuan Fu
2020-09-05 15:53 ` Philipp Stephani [this message]
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