On 2/29/08, Marco Antoniotti <marcoxa@cs.nyu.edu> wrote:
There is no stating in the ANSI spec that ARRAY-DIMENSION-LIMIT = or / = or < or <= ARRAY-TOTAL-SIZE-LIMIT. AFAIU, the latter is guaranteed to be the maximum number of elements in an array as per the glossary entry about "array total size" (always implementation dependent).
From the ARRAY-TOTAL-SIZE-LIMIT dictionary entry:
"The actual limit on the array total size imposed by the implementation might vary according the element type of the array; in this case, the value of array-total-size-limit will be the smallest of these possible limits." which IMO makes it unsuitable for this type. ARRAY-DIMENSION-LIMIT OTOH doesn't carry these weasel-words, which in my interpretation means that it is the greatest of the possible limits. (But the distinction is somewhat academic, I grant you. In eg. SBCL both A-D-L and A-T-S-L are MOST-POSITIVE-FIXNUM, though arguably at least A-T-S-L should be smaller then that.)
The real issue I am not sure about is whether to include or not the limit. It has been known for DOTIMES to expand in such a way to make the counter (at least internally) reach the limit.
In that I would prefer another name -- since ARRAY-INDEX is not a descriptive one anymore. ARRAY-DIMENSION would be more correct then.
In any case that was my unstated rationale for the definition. If people are more confortable using ARRAY-DIMENSION-LIMIT. In this case, I think the definition should look like
(deftype array-index () `(integer 0 (,array-dimension-limit)))
as A-D-L is already the upper exclusive limit.
...for dimension, not index. :) Cheers, -- Nikodemus