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master 756b7cf5d9: Mention caveats in the map-delete doc string
From: |
Lars Ingebrigtsen |
Subject: |
master 756b7cf5d9: Mention caveats in the map-delete doc string |
Date: |
Tue, 26 Apr 2022 09:34:32 -0400 (EDT) |
branch: master
commit 756b7cf5d9a817503437b3e8a9e8d912b7ee6c75
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>
Mention caveats in the map-delete doc string
* lisp/emacs-lisp/map.el (map-delete): Mention how this has to be
used for lists (bug#25929).
---
lisp/emacs-lisp/map.el | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/lisp/emacs-lisp/map.el b/lisp/emacs-lisp/map.el
index c53f253f87..8c67d7c7a2 100644
--- a/lisp/emacs-lisp/map.el
+++ b/lisp/emacs-lisp/map.el
@@ -175,7 +175,17 @@ MAP can be an alist, plist, hash-table, or array."
(cl-defgeneric map-delete (map key)
"Delete KEY in-place from MAP and return MAP.
-Keys not present in MAP are ignored.")
+Keys not present in MAP are ignored.
+
+Note that if MAP is a list (either alist or plist), and you're
+deleting the final element in the list, the list isn't actually
+destructively modified (but the return value will reflect the
+deletion). So if you're using this method on a list, you have to
+say
+
+ (setq map (map-delete map key))
+
+for this to work reliably.")
(cl-defmethod map-delete ((map list) key)
;; FIXME: Signal map-not-inplace i.s.o returning a different list?
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