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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Wed, 13 Mar 2013 21:54:31 +0100
Organization: cbb software GmbH
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Date: 2013-03-13T21:54:31+01:00
List-Id: <comp.lang.ada>

On Wed, 13 Mar 2013 19:54:22 +0000, Simon Wright wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On Wed, 13 Mar 2013 17:45:56 +0000, Simon Wright wrote:
>>
>>> I don't remember ever using 'Pred/'Succ,
>>
>> Even in:
>>
>> generic
>>    type Discrete is (<>);
>> package Foo is
> 
> Nope.
> 
> Out of over 200 packages I have only one with this construct: it is a
> signature package, no need for 'Pred or 'Succ (in other words, the
> enumeration defines a set of distinct possibilities, ordering
> irrelevant).

You need (<>) as an ancestor of both mod <> and range <> in packages that
should be instantiated with either integer or modular type.

Ada needs explicit interfaces, so that you could declare an unordered
enumeration if you don't need order. However, from the practical
perspective that would be public view, privately you still need it ordered
in some ad-hoc way to be able to implement stream attributes, hash tables
etc.

P.S. This is how Ada could finally get curly brackets  (:-)):

   type Color is {Red, Green, Blue}; -- No order in public views

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