dolist vs mapcar

dashtest.el

;;; dashtest.el --- benchmarking dash  -*- lexical-binding: t -*-

(defmacro --map-mapcar (form list)
  (declare (debug (form form)))
  `(mapcar (lambda (_) ,form) ,list))

(defmacro --map-loop (form list)
  (declare (debug (form form)))
  (let ((result-sym (make-symbol "result")))
    `(let (,result-sym)
       (dolist (_ ,list)
         (push ,form ,result-sym))
       (nreverse ,result-sym))))

(defun wh/benchmark ()
  (interactive)
  (let ((small-list (make-list 1 'foo))
        (medium-list (make-list 1000 'foo))
        (large-list (make-list 100000 'foo))
        (it nil))
    (message
     "Small list with mapcar (seconds):\t%f"
     (car (benchmark-run 100 (--map-mapcar it small-list))))
    (message
     "Small list with loop (seconds):\t\t%f"
     (car (benchmark-run 100 (--map-loop it small-list))))
    (message
     "Medium list with mapcar (seconds):\t%f"
     (car (benchmark-run 100 (--map-mapcar it medium-list))))
    (message
     "Medium list with loop (seconds):\t%f"
     (car (benchmark-run 100 (--map-loop it medium-list))))
    (message
     "Large list with mapcar (seconds):\t%f"
     (car (benchmark-run 100 (--map-mapcar it large-list))))
    (message
     "Large list with loop (seconds):\t\t%f"
     (car (benchmark-run 100 (--map-loop it large-list))))))

;; Small list with mapcar (seconds):	0.000055
;; Small list with loop (seconds):	0.000018
;; Medium list with mapcar (seconds):	0.022790
;; Medium list with loop (seconds):	0.020532
;; Large list with mapcar (seconds):	1.625413
;; Large list with loop (seconds):	2.269947