The improved Swift code shown in the original post takes 0.5s to compile with optimizations on my system. It runs in 4-5us per inner loop. The following Common

The improved Swift code shown in the original post takes 0.5s to compile with optimizations on my system. It runs in 4-5us per inner loop. The following Common Lisp code: (defun bench-array () (declare (optimize (speed 3) (debug 0) (safety 1))) (let ((arr (make-array 3000))) (declare (dynamic-extent arr)) ; stack allocate (loop :with sum fixnum = 0 :for i fixnum :from 0 :repeat 15 :do (time (setf sum (loop :for k fixnum :from 0 :repeat 3000 :do (setf (aref arr k) i) :finally (return (loop :for l fixnum :across arr :sum l fixnum))))) (print sum)))) compiles in 0.01s and runs in 5us per inner loop on my system (SBCL). It has array bounds checking enabled (safety 1 declaration). If I remove it (safety 0), runtime improves to 2-3us per inner loop. I'll take Common Lisp over Swift any day of the week :-]