GNU bug report logs - #70524
[PATCH] Fix `map-elt` with `setf` for subplaces

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From: Okamsn <okamsn <at> protonmail.com>
To: 70524 <at> debbugs.gnu.org
Subject: bug#70524: [PATCH] Fix `map-elt` with `setf` for subplaces
Date: Tue, 23 Apr 2024 02:10:42 +0000

[Message part 1 (text/plain, inline)]

Hello,

Currently, the use

     (let ((arr (vector 0 1 2 3 4 5 6)))
       (setf (map-elt (cl-subseq arr 3) 0)
             27)
       arr)

expands to

     (let ((arr (vector 0 1 2 3 4 5 6)))
       (let* ((v arr))
         (condition-case nil
             (with-no-warnings
               (map-put! (cl-subseq v 3) 0 27 nil))
           (map-not-inplace
            (let* ((new (map-insert (cl-subseq v 3) 0 27)))
              (progn
                (cl-replace v new :start1 3 :end1 nil)
                new))
            27)))
       arr)

which does not modify the original variable `arr` due to how `map-put!` 
is being used. With the attached patch, it would expand to

     (let ((arr (vector 0 1 2 3 4 5 6)))
       (let* ((v arr))
         (condition-case nil
             (with-no-warnings
               (let* ((m (cl-subseq v 3)))
                 (progn
                   (map-put! m 0 27 nil)
                   (let* ((new m))
                     (progn
                       (cl-replace v new :start1 3 :end1 nil)
                       new))
                   27)))
           (map-not-inplace
            (let* ((new (map-insert (cl-subseq v 3) 0 27)))
              (progn
                (cl-replace v new :start1 3 :end1 nil)
                new))
            27)))
       arr)

which correctly sets the value using `cl-replace` as the setter for 
`cl-subseq`.

Thank you.

[0001-Make-setf-with-map-elt-work-with-subplaces.patch (text/x-patch, attachment)]

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