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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Quantified expressions: no support for restriction predicates
Date: Mon, 30 Apr 2012 21:48:59 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2012-04-30T21:48:59-05:00
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"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wcc7gwywcuh.fsf@shell01.TheWorld.com...
> phil.clayton@lineone.net writes:
>
>> Is that actually possible for a Dynamic_Predicate?  Section 3.2.4 Subtype 
>> Predicates, para 27/3 says:
>>
>>   The discrete_subtype_definition of a loop_parameter_specification
>>   shall not denote ... or any subtype to which Dynamic_Predicate
>>   specifications apply.
>
> Yeah, I think you're right.  The idea is that we didn't want hidden
> inefficiencies.
>
>    type T is new Integer with
>        Dynamic_Predicate => T mod 10_000 = 0;
>    for X in T loop -- Illegal!
>
> If that were legal, it would probably be grossly inefficient.

Especially if Integer is a 64-bit type in this implementation. :-) My 
examples of this problem always used Long_Integer for this reason:

    type T is new Long_Integer with
        Dynamic_Predicate => T mod 2**30 = 0;
    for X in T loop -- Illegal!

                                        Randy.