Add a faster seq-uniq for lists

* lisp/emacs-lisp/seq.el (seq-uniq): Add a faster method for lists
(bug#57079).

1 files changed, 17 insertions, 0 deletions

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index 1b8d86563a1..6ddd8de6e8d 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -455,6 +455,23 @@ TESTFN is used to compare elements, or `equal' if TESTFN is nil."
         (setq result (cons elt result))))
     (nreverse result)))
 
+(cl-defmethod seq-uniq ((sequence list) &optional testfn)
+  (let ((result nil))
+    (if (not testfn)
+        ;; Fast path.
+        (while sequence
+          (unless (member (car sequence) result)
+            (push (car sequence) result))
+          (pop sequence))
+      ;; Slower path.
+      (while sequence
+        (unless (seq-find (lambda (elem)
+                            (funcall testfn elem (car sequence)))
+                          result)
+          (push (car sequence) result))
+        (pop sequence)))
+    (nreverse result)))
+
 (cl-defgeneric seq-mapcat (function sequence &optional type)
   "Concatenate the result of applying FUNCTION to each element of SEQUENCE.
 The result is a sequence of type TYPE, or a list if TYPE is nil."