I have been told to avoid linked lists.

I've been told to avoid linked lists because their elements are scattered everywhere, which can be true in some cases. However, I wonder what happens in loops, which I use frequently. I tried to inspect memory addresses of list elements of these two programs run on SBCL. CL-USER> (setq a-list (let ((a nil)) (push 10 a) (push 20 a) (push 30 a) a)) (30 20 10) CL-USER> (sb-kernel:get-lisp-obj-address a-list) 69517814583 (37 bits, #x102F95AB37) CL-USER> (sb-kernel:get-lisp-obj-address (cdr a-list)) 69517814567 (37 bits, #x102F95AB27) CL-USER> (sb-kernel:get-lisp-obj-address (cddr a-list)) 69517814551 (37 bits, #x102F95AB17) CL-USER> (sb-kernel:get-lisp-obj-address (cddr a-list)) 69517814551 (37 bits, #x102F95AB17) CL-USER> (setq a-list (let ((a nil)) (push 10 a) (push 20 a) (push 30 a) a)) (30 20 10) CL-USER> (sb-kernel:get-lisp-obj-address a-list) 69518319943 (37 bits, #x102F9D6147) CL-USER> (sb-kernel:get-lisp-obj-address (cdr a-list)) 69518319927 (37 bits, #x102F9D6137) CL-USER> (sb-kernel:get-lisp-obj-address (cddr a-list)) 69518319911 (37 bits, #x102F9D6127) In both programs, the list elements are not scattered. So, if scattered list elements were an issue for these simple cases, you probably used the wrong compiler or memory allocator.

Mar 23, 2025 - 09:47

I've been told to avoid linked lists because their elements are scattered everywhere, which can be true in some cases. However, I wonder what happens in loops, which I use frequently. I tried to inspect memory addresses of list elements of these two programs run on SBCL.

CL-USER> (setq *a-list* (let ((a nil)) (push 10 a) (push 20 a) (push 30 a) a))
(30 20 10)
CL-USER> (sb-kernel:get-lisp-obj-address *a-list*)
69517814583 (37 bits, #x102F95AB37)
CL-USER> (sb-kernel:get-lisp-obj-address (cdr *a-list*))
69517814567 (37 bits, #x102F95AB27)
CL-USER> (sb-kernel:get-lisp-obj-address (cddr *a-list*))
69517814551 (37 bits, #x102F95AB17)
CL-USER> (sb-kernel:get-lisp-obj-address (cddr *a-list*))
69517814551 (37 bits, #x102F95AB17)

CL-USER> (setq *a-list* (let ((a nil))
              (push 10 a)
              (push 20 a)
              (push 30 a) 
              a))
(30 20 10)
CL-USER> (sb-kernel:get-lisp-obj-address *a-list*)
69518319943 (37 bits, #x102F9D6147)
CL-USER> (sb-kernel:get-lisp-obj-address (cdr *a-list*))
69518319927 (37 bits, #x102F9D6137)
CL-USER> (sb-kernel:get-lisp-obj-address (cddr *a-list*))
69518319911 (37 bits, #x102F9D6127)

In both programs, the list elements are not scattered. So, if scattered list elements were an issue for these simple cases, you probably used the wrong compiler or memory allocator.