Re: Is this expected behavior or not

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:8klywqh2pf$.1f949flc1xeia.dlg@40tude.net...
> On Tue, 12 Mar 2013 13:19:06 -0400, Robert A Duff wrote:
...
>>>    for I in Prime'Range loop -- What is this supposed to mean?
>>>       ...
>>
>> It doesn't mean anything -- it's illegal.
>
> Why Prime'Succ is legal then?

You could argue that it should have been. But as it is an operation on a 
type, not a subtype, constraints and predicates aren't involved, so it 
doesn't need to be illegal.

> And what about:
>
>   for I in Prime'First..Prime'Last loop

'First and 'Last are also illegal on subtypes that have predicates. (See 
3.2.4(26/3)). I argued that this is wrong, in that these are also operations 
returning values of the base type. The above means:

    for I in Prime'Base range Prime'First .. Prime'Last loop

and that is quite meaningful. But there was concern over confusing this with

    for I in Prime loop

which clearly involves the subtype.

Making 'First and 'Last illegal also ties in with the impossibility of 
having an array indexed by a subtype with a predicate (which is nearly 
impossible to implement, especially because of the possibility of slices). 
That had to be illegal and the related features were carried along.

                                           Randy.