Re: Concatenate enumeration

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

On Wed, 25 Nov 2009 16:53:07 -0600, Randy Brukardt wrote:

> "Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
> news:wcctywksu8t.fsf@shell01.TheWorld.com...
> ...
>>> You can't. Enumeration types are not extensible.
>>
>> Extensible enumeration types were proposed for Ada 9X,
>> but were dropped.
> 
> And were proposed again for Ada 2005, and were dropped again. See 
> AI95-0261-1. I doubt it will ever be proposed again.

These are different things. I think the OP didn't want an extensible type.
He wanted a new independent type constructed in some specific way.

To extend an enumeration type E that has to have the class (E'Class). This
is a lot of work.

To reuse names of the literals of E in some other type, you only need
reflection. E.g. an attribute, say, E'Domain, which would return
"universal-set" of its literals, then you could write:

   type E is (None, Ready);
   type E1 is E'Domain or (Off); -- = (None, Ready, Off)

Not very useful, but in other cases reflection could be very interesting.
For example, in generics:

   generic
      type T is array; -- Only this
   package ... is
      -- The [first] array index type would be T'Index (1)
      -- The array element type would be T'Element etc

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