common lisp 的访问器 FILL-POINTER

fill-pointer.txt

语法
  fill-pointer vector => fill-pointer
  (setf (fill-pointer vector) new-fill-pointer)

参数和值
  vector --- 一个 vector
  fill-pointer, new-fill-pointer --- 一个有效的 fill pointer

描述
  访问 vector 的 fill pointer

代码
  * (setq a (make-array 8 :fill-pointer 4))
  #(0 0 0 0)

  * (fill-pointer a)
  4

  * (dotimes (i (length a)) (setf (aref a i) (* i i)))
  NIL

  * a
  #(0 1 4 9)

  * (setf (fill-pointer a) 3)
  3

  * (fill-pointer a)
  3

  * a
  #(0 1 4)
  
  * (setf (fill-pointer a) 8)
  8

  * a
  #(0 1 4 9 0 0 0 0)