Add cl-with-accessors

* lisp/emacs-lisp/cl-macs.el (cl-with-accessors): New macro.
* doc/misc/cl.texi (Structures): Mention the new macro.
* test/lisp/emacs-lisp/cl-macs-tests.el (cl-lib-struct-with-accessors):
New Test.
* etc/NEWS (New macro 'cl-with-accessors'.): Mention the macro.

This macro is useful when making repeated use of a structures accessor
functions, such as reading from a slot and then writing to a slot.  It
is similar to 'with-slots' from EIEIO, but uses accessor functions
instead of slot names.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/cl-macs-tests.el b/test/lisp/emacs-lisp/cl-macs-tests.el
index b4b939d3d31..ed6b1c2e4d4 100644
--- a/test/lisp/emacs-lisp/cl-macs-tests.el
+++ b/test/lisp/emacs-lisp/cl-macs-tests.el
@@ -541,6 +541,21 @@ collection clause."
   (should (mystruct-p (cl-lib--con-1)))
   (should (mystruct-p (cl-lib--con-2))))
 
+(ert-deftest cl-lib-struct-with-accessors ()
+  (let ((x (make-mystruct :abc 1 :def 2)))
+    (cl-with-accessors ((abc mystruct-abc)
+                        (def mystruct-def))
+        x
+      (should (= abc 1))
+      (should-error (setf abc 99))
+      (should (= def 2))
+      (setf def 3)
+      (should (= def 3))
+      (setq def 4)
+      (should (= def 4)))
+    (should (= 4 (mystruct-def x)))
+    (should (= 1 (mystruct-abc x)))))
+ 
 (ert-deftest cl-lib-arglist-performance ()
   ;; An `&aux' should not cause lambda's arglist to be turned into an &rest
   ;; that's parsed by hand.