Re: Community Input for the Maintenance and Revision of the Ada Programming Language

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-09-03 12:32, Alejandro R. Mosteo wrote:

> And is there a difference to using rename?:

Yes, because renaming does not touch bounds even if explicitly required 
by the subtype.

It is clear why renaming to a subtype does not slide bounds. That is 
because Ada treat a subtype as a constraint. For the same reason it is 
not illegal have such a renaming, that appears to the reading as bound 
sliding.

What was a language design bug that the new constraint is not enforced. 
The program should raise Constraint_Error when the index is outside the 
new bounds, even if wihin the original bounds.

Surely that would be useless behavior, but that is what follows from the 
Ada's subtype definition. One cannot have both.

> (I was actually surprised that you can't explicitly write 
> Zero_Array(Item) with renames).

I am in favor of changing subtypes to be more flexible with the 
representation.

An alternative would be allowing renaming to another type:

    type Array_Type is array (Integer range <>) of Float;

    procedure Foo (A : Array_Type) is
       type Zero_Array is array (Unsigned range <>) of Float;
       B : Zero_Array renames A;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de