Re: Private discrete type as index

[tmoran@acm.org]

>> >>   type x is limited private;
>> >>   type test is array(x) of boolean;
>> >   The "array" abstraction has certain characteristics, among them
>> > sequential indexing.
>> Why so? Array is just a mapping index->element, so if no index ranges
>I suppose the answer will be that index ranges *are* required
>by the array semantics (in Ada, at least). But, as you pointed out:
  Perhaps to some people an array is a general map, but to me, and
to at least the on-line glossaries I checked, it's not that general.
Your abstraction appears to be a general mapping from elements of
some set to booleans.  Type "x" might be character strings and
Test(x) True iff a symbol table has seen that string before.  That's
a perfectly good map, but, IMHO, not something well modeled as an array.
  My point is that your abstract object doesn't match the idea of
"array" sufficiently well, and thus probably shouldn't be implemented
with an array.