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| 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.

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