Re: Private discrete type as index

["AG" <ang@xtra.co.nz>]

<tmoran@acm.org> wrote in message news:adUV9.20206$hl1.1562@sccrnsc04...
> >> Why so? Array is just a mapping index->element, so if no index ranges
[ This was not my quote, I was responding to it ...]

> >I suppose the answer will be that index ranges *are* required
> >by the array semantics (in Ada, at least)

>   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.

No. What I was originally trying to do was an abstraction as close
to the array as possible (booleans do not matter of course - just
something to put there). At the same time, I wanted to restrict
control of the index to the package implementing it (again, as
much as possible).

So, while I realise I can't (in Ada) provide things like "..",  I can
provide +/-/</> operations of varying flavours on the index. This
would keep most (not all, but most) of the array semantics in place.
Unfortunately, this appears to be impossible.

  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.