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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Q: Line_IO
Date: Mon, 31 Aug 2009 21:08:03 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2009-08-31T21:08:03-04:00
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Georg Bauhaus <see.reply.to@maps.futureapps.de> writes:

> Georg Bauhaus wrote:
>>    procedure Print_2 (Item : String) is
>>       subtype Index is Stream_Element_Offset range
>>         Stream_Element_Offset(Item'First)
>>         .. Stream_Element_Offset(Item'Last);
>>       subtype XBytes is Stream_Element_Array (Index);
>>       Item_Bytes: XBytes;
>>       for Item_Bytes'Address use Item'Address;
>>    begin
>>       Stream_IO.Write (Stdout, Item_Bytes);
>>       Stream_IO.Write (Stdout, Separator_Bytes);
>>    end Print_2;
>
> *** line_io.ada	old
> --- line_io.ada	new
> ***************
> *** 78,79 ****
> --- 78,80 ----
>         Item_Bytes: XBytes;
> +       pragma Import (Ada, Item_Bytes);
>         for Item_Bytes'Address use Item'Address;

The Import is not strictly necessary, because Stream_Element_Array has
no default initialization.  But it's still good style -- it says, the
declaration of Item_Bytes is not creating a new object, it's just
overlaying an old one.

If Item_Bytes had default inits (e.g. if it were an array of access
values, which are default-initialized to null, or an array of records
with some defaulted components), then the Import would be necessary.
I think in that case, GNAT warns, because without the Import, the
default inits will overwrite Item, which is certainly not what you
want.

- Bob