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array-has-fill-pointer-p

array-has-fill-pointer-p Function

Syntax:

array-has-fill-pointer-p array → generalized-boolean

Arguments and Values:

array—an array.

generalized-boolean—a generalized boolean.

Description:

Returns true if array has a fill pointer ; otherwise returns false.

Examples:

(array-has-fill-pointer-p (make-array 4)) → implementation-dependent 
(array-has-fill-pointer-p (make-array ’(2 3))) → false 
(array-has-fill-pointer-p 
 (make-array 8 
	     :fill-pointer 2 
	     :initial-element ’filler)) → true


Exceptional Situations:

Should signal an error of type type-error if its argument is not an array.

See Also:

make-array, fill-pointer

Notes:

Since arrays of rank other than one cannot have a fill pointer , array-has-fill-pointer-p always returns nil when its argument is such an array.

Expanded Reference: array-has-fill-pointer-p​

Basic Usage​

array-has-fill-pointer-p returns true if the array has a fill pointer, false otherwise.

(array-has-fill-pointer-p (make-array 5 :fill-pointer 0))
=> T

(array-has-fill-pointer-p (make-array 5 :fill-pointer 3))
=> T

;; Fill pointer set to T (equals total size)
(array-has-fill-pointer-p (make-array 5 :fill-pointer t))
=> T

Arrays Without Fill Pointers​

Simple arrays created without :fill-pointer may or may not have a fill pointer, depending on the implementation.

;; Multi-dimensional arrays never have fill pointers
(array-has-fill-pointer-p (make-array '(2 3)))
=> NIL

;; Strings and bit vectors as literals typically do not
(array-has-fill-pointer-p "hello")
=> NIL

Guarding fill-pointer Calls​

Use array-has-fill-pointer-p before calling fill-pointer to avoid errors.

(defun safe-fill-pointer (array)
  "Return the fill pointer if present, or NIL."
  (when (array-has-fill-pointer-p array)
    (fill-pointer array)))

(safe-fill-pointer (make-array 5 :fill-pointer 3))
=> 3

(safe-fill-pointer (make-array 5))
=> NIL

Only Vectors Can Have Fill Pointers​

Arrays of rank other than 1 never have fill pointers.

(list (array-has-fill-pointer-p (make-array '(3 4)))
      (array-has-fill-pointer-p (make-array '(2 3 4)))
      (array-has-fill-pointer-p (make-array '())))
=> (NIL NIL NIL)