array-displacement

ToC

Allegro CL

ANSI Common Lisp

15 Arrays

15.2 Dictionary of Arrays

15.2.15 array-displacement

Function

Syntax:

array-displacement array

displaced-to, displaced-index-offset

Arguments and Values:

array - an array.

displaced-to - an array or nil.

displaced-index-offset - a non-negative fixnum.

Description:

If the array is a displaced array, returns the values of the :displaced-to and :displaced-index-offset options for the array (see the functions make-array and adjust-array). If the array is not a displaced array, nil and 0 are returned.

If array-displacement is called on an array for which a non-nil object was provided as the :displaced-to argument to make-array or adjust-array, it must return that object as its first value. It is implementation-dependent whether array-displacement returns a non-nil primary value for any other array.

Examples:

 (setq a1 (make-array 5))  #<ARRAY 5 simple 46115576>
 (setq a2 (make-array 4 :displaced-to a1
                        :displaced-index-offset 1))
 #<ARRAY 4 indirect 46117134>
 (array-displacement a2)
 #<ARRAY 5 simple 46115576>, 1
 (setq a3 (make-array 2 :displaced-to a2
                        :displaced-index-offset 2))
 #<ARRAY 2 indirect 46122527>

 (array-displacement a3)
 #<ARRAY 4 indirect 46117134>, 2

Exceptional Situations:

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

See Also:

make-array

Allegro CL Implementation Details:

None.