From 4b762015ebb82d1861c2efe51c1e902ac329bc8e Mon Sep 17 00:00:00 2001
From: Adam Porter <adam@alphapapa.net>
Date: Fri, 8 Mar 2024 23:43:14 -0600
Subject: [PATCH] (vtable-update-object): Make old-object argument optional
 (Bug#69666)

* lisp/emacs-lisp/vtable.el (vtable-update-object): Make 'old-object'
argument optional.
* doc/misc/vtable.texi (Interface Functions): Update documentation.
* etc/NEWS: Add news entry.

It's often necessary to update the representation of a single object in
a table (e.g a struct, whose identity does not change when its slots'
values are changed).  To do so, now the function may be called like
this:

  (vtable-update-object table object)

Instead of like this:

  (vtable-update-object table object object)
---
 doc/misc/vtable.texi      | 9 ++++++---
 etc/NEWS                  | 9 +++++++++
 lisp/emacs-lisp/vtable.el | 9 +++++++--
 3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/doc/misc/vtable.texi b/doc/misc/vtable.texi
index a4f2ed29d93..6881e9663c4 100644
--- a/doc/misc/vtable.texi
+++ b/doc/misc/vtable.texi
@@ -554,9 +554,12 @@ Interface Functions
 also updates the displayed table.
 @end defun
 
-@defun vtable-update-object table object old-object
-Change @var{old-object} into @var{object} in @var{table}.  This also
-updates the displayed table.
+@defun vtable-update-object table object &optional old-object
+Update @var{object}'s representation in @var{table}.  Optional argument
+@var{old-object}, if non-@code{nil}, means to replace @var{old-object}
+with @var{object} and redisplay the associated row in the table.  In
+either case, if the existing object is not found in the table (being
+compared with @code{equal}), signal an error.
 
 This has the same effect as calling @code{vtable-remove-object} and
 then @code{vtable-insert-object}, but is more efficient.
diff --git a/etc/NEWS b/etc/NEWS
index a654d2d8d79..85751074aaa 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2175,6 +2175,15 @@ aforementioned functions:
     (and (arrayp executing-kbd-macro)
          (>= executing-kbd-macro-index (length executing-kbd-macro))))
 
++++
+** 'vtable-update-object' updates an existing object with just two arguments.
+It is now possible to update the representation of an object in a vtable
+by calling 'vtable-update-object' with just the vtable and the object as
+arguments.  (Previously the 'old-object' argument was required which, in
+this case, would mean repeating the object in the argument list.)  When
+replacing an object with a different one, passing both the new and old
+objects is still necessary.
+
 
 * Changes in Emacs 30.1 on Non-Free Operating Systems
 
diff --git a/lisp/emacs-lisp/vtable.el b/lisp/emacs-lisp/vtable.el
index 15a430f5c26..dfcfa434135 100644
--- a/lisp/emacs-lisp/vtable.el
+++ b/lisp/emacs-lisp/vtable.el
@@ -283,8 +283,13 @@ vtable-goto-column
       (goto-char (prop-match-beginning match))
     (end-of-line)))
 
-(defun vtable-update-object (table object old-object)
-  "Replace OLD-OBJECT in TABLE with OBJECT."
+(defun vtable-update-object (table object &optional old-object)
+  "Update OBJECT's representation in TABLE.
+When OLD-OBJECT is non-nil, replace OLD-OBJECT with OBJECT and display
+it.  In either case, if the existing object is not found in the
+table (being compared with `equal'), signal an error."
+  (unless old-object
+    (setq old-object object))
   (let* ((objects (vtable-objects table))
          (inhibit-read-only t))
     ;; First replace the object in the object storage.
-- 
2.30.2