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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Streams in GNAT 3.14p
Date: Wed, 12 Jun 2002 10:43:56 +0200
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Date: 2002-06-12T10:43:56+02:00
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On 10 Jun 2002 12:14:41 -0700, dennison@telepath.com (Ted Dennison)
wrote:

>Dmitry A.Kazakov <mailbox@dmitry-kazakov.de> wrote in message news:<ae295a$3b12g$1@ID-77047.news.dfncis.de>...
>> Hi!
>> 
>> Recently I found that GNAT 3.14p implementation of streams looks a bit 
>> strange. When a tagged object is written (S'Class'Output), then 
>> Write(Stream, Item) is called for each character of the external 
>> representation of tag _separately_. For types declared in deeply nested 
>> child packages it is about 100 separate calls.
>
>That's the way String'Output (and any other array 'Output) works by
>default. I suppose they could have optimized it for tag strings
>without running afowl of the ARM, but it isn't horribly suprising that
>they didn't.

I think that a possible way to make Streams usable for internal
communication could be [in the future standard] to declare two
dispatching operations for Root_Stream_Type dealing with tags:

procedure Output (Stream : access Root_Stream_Type; Type_Tag : Tag); 
function Input (Stream : access Root_Stream_Type) return Tag; 

They use Ada.Tags.External_Tag/Internal_Tag if not overridden. Then a
user could override them with something like:

procedure Output
   (Stream : access Local_Memory_Stream; Type_Tag : Tag) is
begin
   Tag'Output (Stream, Type_Tag);
end Output;

function Input (Stream : access Local_Memory_Stream) return Tag is
begin
   return Tag'Input (Stream);
end Input;

Of course Tag'Input and Tag'Output should have reasonable
implementations, i.e. input/output tags as-is.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de