Re: about inheritance of subtypes and entities (such as constants) related to a type in the same package

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

On 2018-05-31 20:53, Dan'l Miller wrote:
> On Thursday, May 31, 2018 at 12:37:07 PM UTC-5, Dmitry A. Kazakov wrote:
>> On 2018-05-31 04:29 PM, Dan'l Miller wrote:
>>> Conversely, subtyping in Ada does none of that type-extension stuff:  no
>>>   additional data/cardinality-of-the-members-of-the-set, no additional
>>   > routines/behavior, no arbitrary refinement of behavior of overridden/copied
>>>   routines/operations.  Instead, subtyping in Ada is strictly subjecting the
>>>   parent type to an additional membership-narrowing predicate, such as subset
>>   > in set theory.  Randy likewise spoke of membership on other branches of this
>>   > thread.
>>
>> Untrue. Ada 83 subtyping extends the supertype (base type), because it
>> exports operations defined on the subtype to the base type. Ada 83
>> subtyping introduces an equivalent type, which is both sub- and
>> supertype of the base.
> 
> If Ada83 untagged subtyping is type extension, please provide even a single characteristic that was extended/added/supplemented instead of contracted/subtracted/elided by the predicate.

Elementary:

    subtype Extension is Integer;
    procedure Extended_Operation (X : Extension) is null;
    X : Integer;
    Y : Extension;
begin
    Extended_Operation (X); -- See #1
    Extended_Operation (Y); -- See #2

The subtype Extension extends Integer with Extended_Operation, which has 
two separate meanings:

1. The base type Integer has now a new operation:

    new Integer interface = old Integer interface + Extended_Operation

2. The subtype Extension extends inherited Integer's set of operations:

    Extended interface = old Integer interface + Extended_Operation

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