util: provide pointer (ptr = (make-array nil)

test/test-core.lisp

@@ -67,6 +67,10 @@
   (util:lgi (crypt:create-secret))
   (let ((now (get-universal-time)))
     (== (util:from-unix-time (util:to-unix-time now)) now))
+  (let* ((x (util:ptr))
+         (y x))
+    (setf (aref y) 42)
+    (== (aref x) 42))
   (== (util:rfill '(1 2 3 4 5) '(a b c)) '(a b c nil nil))
   (== (util:rtrim '(1 2 nil 3 nil)) '(1 2 nil 3)) 
   (== (util:to-keyword "hello-kitty") :hello-kitty)

util/util.lisp

@@ -6,6 +6,7 @@
   #+sbcl (:import-from :sb-ext #:add-package-local-nickname)
   (:export #:make-vars-format #:lg #:lgd #:lgi #:lgw
            #:from-unix-time #:to-unix-time
+           #:ptr
            #:rfill #:rtrim 
            #:loop-plist #:filter-plist #:plist-pairs #:plist-equal #:plist-add
            #:flatten-str #:from-keyword #:to-keyword #:to-integer #:to-string
@@ -41,7 +42,10 @@
 (defun to-unix-time (time)
   (when time (- time +unix-time-base+)))
 
-;;;; lists and loops
+;;;; pointers, lists, loops
+
+(defun ptr (&optional x) 
+  (make-array nil :initial-element x))
 
 (defun rfill (ll ls)
   (mapcar #'(lambda (x) (pop ls)) ll))