Re: syntaxic exploration

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 17-12-24 05:37 , Robert Eachus wrote:
> On Saturday, December 23, 2017 at 11:23:32 AM UTC-5, Jeffrey R.
> Carter wrote:
>> On 12/22/2017 11:11 PM, Niklas Holsti wrote:
>>>
>>> I think the aggregate form (null array) was suggested some time
>>> ago, in analogy with the existing (null record). It looks good to
>>> me, but as I remember, there was some objection. One problem is
>>> that if the index type has exactly one value, then a null array
>>> with that index type cannot exist (because then A'First = A'Last
>>> for any such array A).

   [snip]

> A more complex, and potentially ugly case is for multidimensional
> arrays.  Defining (null array) as being empty in all dimensions with
> Foo'Range(n) = Bar'First..Bar'Pred(Bar'First) where Bar is the nth
> index SUBtype for Foo works.

In other words, the same as the current rule for the null string literal "".

> In general, you should be surprised if Foo'Last(N) for a null
> array doesn't raise Constraint_Error.

That is not true in current Ada, as I understand it.

That would be very bad -- it would mean that any general operation that 
loops over an array that is potentially null would have to first check 
the 'Length. Fortunately this is not the case.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .