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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: A few questions
Date: Tue, 3 Nov 2015 00:33:46 -0600
Organization: JSA Research & Innovation
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Date: 2015-11-03T00:33:46-06:00
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"Simon Wright" <simon@pushface.org> wrote in message 
news:ly1tc8me4w.fsf@pushface.org...
> Simon Wright <simon@pushface.org> writes:
>
>> I'd have liked to support
>>
>>    for D in Period loop
>
> Oops, I meant "for D of Period", i.e.
>
>   for D : Ada.Calendar.Time of Period loop
>      ...
>
> but you'd need
>
>   function Constant_Reference
>     (Container : aliased Date_Container;
>      Position  : Cursor) return Constant_Reference_Type;
>
> returning
>
>   type Constant_Reference_Type
>      (Element : not null access constant Ada.Calendar.Time) is private
>   with
>      Implicit_Dereference => Element;
>
> which is clearly meant for actual containers and here would require - I
> think - allocating an Ada.Calendar.Time, and of course freeing it
> eventually.
>
> Shame, it makes it tricky to support lazy evaluation. But perhaps we
> shouldn't want to ...

If you *only* need constants, the Constant_Indexing function can be a normal 
function (no implicit dereference required). In that case, the 
implementation will do the memory management. Note the difference in wording 
between 4.1.6(2/3) and 4.1.6(3/3) (there is no requirement on the return 
type for Constant_Indexing).

OTOH, I think GNAT got that wrong somehow when I constructed an ACATS test 
to try that (don't recall the details). So it may not work in your copy of 
GNAT, most likely it will in a future version.

                                       Randy.