GNU bug report logs - #36418
26.2.90; mapconcat "SEPARATOR must be a string." is incorrect

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Package: emacs;

Reported by: Xu Chunyang <mail <at> xuchunyang.me>

Date: Fri, 28 Jun 2019 13:24:02 UTC

Severity: minor

Found in version 26.2.90

Done: Eli Zaretskii <eliz <at> gnu.org>

Bug is archived. No further changes may be made.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Xu Chunyang <mail <at> xuchunyang.me>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.2.90; mapconcat "SEPARATOR must be a string." is incorrect
Date: Fri, 28 Jun 2019 21:23:24 +0800

C-h f mapconcat says

> SEPARATOR must be a string.

but nil works fine

    (mapconcat #'identity '("a" "b") nil)
    ;; => "ab"

and `string-join` relies on this fact (by the way, string-join's
docstring doesn't explain the case when separator is omitted or nil)

    (defsubst string-join (strings &optional separator)
      "Join all STRINGS using SEPARATOR."
      (mapconcat 'identity strings separator))

C-h S mapconcat says

> SEPARATOR, which also must be a string, or a vector or list of
> characters.

C-h f concat says

> Each argument may be a string or a list or vector of characters (integers).
This bug report was last modified 5 years and 323 days ago.

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