Ada.Streams.Stream_IO.File_Type

Ada.Streams.Stream_IO.File_Type

[tmoran]

Why is this not a descendant of Ada.Finalization.Limited_Controlled?

Re: Ada.Streams.Stream_IO.File_Type

[Craig Carey]

On Tue, 15 Jul 2003 20:13:37 GMT, tmoran@acm.org wrote:

---------------------------
>Why is this [Ada.Streams.Stream_IO.File_Type] not a descendant of
>  Ada.Finalization.Limited_Controlled?
---------------------------

That would be done to allow no call to Close(). Close might raise errors.
 GNAT's already code has the doubly linked list (in GNAT-'only' package
 System.File_Control_Block).

---

From another thread (mis)titled "Re: Terminating a task"

It was on the 2nd computer language shootout contest:
  http://dada.perl.it/shootout/  (wc example: counting words in binary)

---------------------------
On Tue, 15 Jul 2003 13:30:33 -0500, "David C. Hoos" 
>The package Ada.TextIO.Text_Streams allows one to obtain the stream
> object corresponding to the standard input -- i.e.:
>
>Standard_Input_Stream : Ada.Text_IO.Text_Streams.Stream_Access =
>   Ada.Text_IO.Text_Streams.Stream (Ada.Text_IO.Standard_Input);
---------------------------

This comment is not on Text_Streams:

---------------------------
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Fill string with multiple lines from standard_input
Date: Fri, 16 Aug 2002 21:26:29 -0500

...
Keep in mind that Stream_IO was virtually untested by the ACATS until
recently, and even now the standard has serious problems which can make
the use of Stream_IO non-portable (since compilers pretty much all do
the wrong thing). So even an implementation which passes the ACATS tests
may still have problems in some cases (having to do with writing, [...]
---------------------------

It is a problem with the design rather than the testing. ACT doesn't
 like the design.

A fix would be to add this next line to Ada.Streams.Stream_IO:

    function Standard_Input return File_Type;

Anyone know why it is not in there already?. Portable Ada programs
 handling piping or CGI I/O may need that unless using C (etc.).

I looked for an AI or comment at Ada-Comment, hinting that a fix is
 desired or intended, but found nothing.

Using C's setmode() and read() seems to be a good solution.

--

Currently GNAT 3.15's Text_IO.Text_Streams feature stops reading, on
 encountering a ASCII.SUB character (= character 10#26#). Presumably
 they don't like the RM's design.

Demo code:   % cat data | tr \\032-\\032 " " | wc
----------------------------------
   type Tio is Ada.Text_IO;
   In_Stream   : Tio.Text_Streams.Stream_Access;
   Out_Stream  : Tio.Text_Streams.Stream_Access;
   Input_Chars : Ada.Streams.Stream_Element_Array (1 .. 1024);
   Last        : Ada.Streams.Stream_Element_Offset;
...
      --  Now use the "do a type conversions on a pointer" package:
   In_Stream := Tio.Text_Streams.Stream (Tio.Current_Input);
   Out_Stream := Tio.Text_Streams.Stream (Tio.Current_Output);
      --  Now use the text package to handle binary I/O:
   loop
      Ada.Streams.Read (In_Stream.all, Input_Chars, Last);
      exit when Last = 0;    --  Quit on the first ASCII.SUB character
      Ada.Streams.Write (Out_Stream.all, Input_Chars (1 .. Last));
   end loop;
----------------------------------


AARM A.12.2: Package Text_IO.Text_Streams:
   http://www.adaic.org/standards/95aarm/html/AA-A-12-2.html

AARM 13.13.1: Package Streams:
   http://www.adaic.org/standards/95aarm/html/AA-13-13-1.html

AARM A.12.1: Package Streams.Stream_IO:
   http://www.adaic.org/standards/95aarm/html/AA-A-12-1.html


______

- Craig Carey

How to Cross-Compiled in FreeBSD to/for a x86 Linux target:
 http://www.ijs.co.nz/code/ada95-freebsd-to-linux-cross-compiler.txt

Re: Ada.Streams.Stream_IO.File_Type

[Nick Roberts]

<tmoran@acm.org> wrote in message news:RfZQa.71833$N7.8631@sccrnsc03...

[of the type Ada.Streams.Stream_IO.File_Type]
> Why is this not a descendant of
> Ada.Finalization.Limited_Controlled?

The visible declaration in the package Ada.Streams.Stream_IO is:

   type File_Type is limited private;

This means that the type is not visibly a descendant of Limited_Controlled,
but it could be implemented by putting:

   type File_Type is new Ada.Finalization.Limited_Controlled with private;

in the private part of package Ada.Streams.Stream_IO. I'm not quite sure if
such an implementation would be criticised on the grounds that objects of
File_Type could not then be declared other than at library level.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]

Re: Ada.Streams.Stream_IO.File_Type

[Nick Roberts]

"Craig Carey" <research@ijs.co.nz> wrote in message
news:mt7chvs7heoihdv7a3a6psh5h8v1b46i2i@4ax.com...

> On Tue, 15 Jul 2003 13:30:33 -0500, "David C. Hoos"
> > The package Ada.TextIO.Text_Streams allows one
> > to obtain the stream object corresponding to the
> > standard input -- i.e.:
> >
> > Standard_Input_Stream :
> >    Ada.Text_IO.Text_Streams.Stream_Access :=
> >       Ada.Text_IO.Text_Streams.Stream
> >          (Ada.Text_IO.Standard_Input);
>
> This comment is not on Text_Streams:
> ...
> A fix would be to add this next line to Ada.Streams.Stream_IO:
>
>     function Standard_Input return File_Type;
>
> Anyone know why it is not in there already?

Yes! Because you can use the technique given by David Hoos.

> Portable Ada programs handling piping or CGI I/O may
> need that unless using C (etc.).

If an Ada program which is a client of the Common Gateway Interface (CGI) --
used by various web (HTTP) server programs to allow 'client' programs to
dyamically generate web pages -- implements the interface by directly
interacting with its 'standard input' and 'standard output' (in the Unix
sense), it must be considered essentially non-portable.

Such a program may be portable among Unix-based (maybe POSIX-based)
environments, but generally not otherwise. In this case, the Ada program
might just as well import the appropriate C functions to read or write bytes
directly; I would suggest that in most cases interaction is all text-based
anyway, and it would be easier and better to use Ada.Text_IO (and if the Ada
implementation isn't able to handle line termination correctly, I would say
that's a major problem with the implementation).

For true portability, an Ada program which is intended to be used as a CGI
client should put everything specific to interfacing with the environment
into a package (named 'CGI' perhaps ;-) and I'm fairly sure at least one
such package is available. To port the program to a (significantly
different) environment, this package (only) needs to be reimplemented. This
would provide further advantageous isolation (such as from changes to the
HTTP header that a CGI client program should output).

> ...
> Currently GNAT 3.15's Text_IO.Text_Streams feature
> stops reading, on encountering a ASCII.SUB character
> (= character 10#26#).

That's just a problem with GNAT, isn't it?

> Presumably they don't like the RM's design.

Presumably it's a simple bug in GNAT 3.15. It's quite reasonable (in my
'humble' opinion :-) for text-oriented I/O (except Look_Ahead and
Get_Immediate) to stop on a SUB, but not stream-oriented I/O. The RM permits
this; I think it would often be handy for Ada implementations to provide
options with regard to line, page, and file termination.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]

Re: Ada.Streams.Stream_IO.File_Type

[Dmitry A. Kazakov]

On Tue, 15 Jul 2003 20:13:37 GMT, tmoran@acm.org wrote:

>Why is this not a descendant of Ada.Finalization.Limited_Controlled?

Probably, because one wished to keep Streams free from tagged types.
(specifications mention only 'Class, but no tagged types).

However, it is brilliant example where interfaces inheritance and
multiple inheritance could be useful: to override a decision made by a
designer, you cannot influence. (:-))

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

Re: Ada.Streams.Stream_IO.File_Type

[Matthew Heaney]

"Nick Roberts" <nickroberts@blueyonder.co.uk> wrote in message news:<bf6jhs$b9l6h$1@ID-25716.news.uni-berlin.de>...
>
> > Anyone know why it is not in there already?
> 
> Yes! Because you can use the technique given by David Hoos.

To which technique are you referring?

Re: Ada.Streams.Stream_IO.File_Type

[David C. Hoos]

----- Original Message ----- 
From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada.eu.org>
Sent: Friday, July 18, 2003 12:34 PM
Subject: Re: Ada.Streams.Stream_IO.File_Type


> "Nick Roberts" <nickroberts@blueyonder.co.uk> wrote in message
news:<bf6jhs$b9l6h$1@ID-25716.news.uni-berlin.de>...
> >
> > > Anyone know why it is not in there already?
> >
> > Yes! Because you can use the technique given by David Hoos.
>
> To which technique are you referring?
He's probable referring to my message of July 15 in the thread
"Terminating a Task."
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada
>

Re: Ada.Streams.Stream_IO.File_Type

[Mário Amado Alves]

> ...
> but it could be implemented by putting:
> 
>    type File_Type is new Ada.Finalization.Limited_Controlled with private;
> 
> in the private part of package Ada.Streams.Stream_IO. I'm not quite sure if
> such an implementation would be criticised on the grounds that objects of
> File_Type could not then be declared other than at library level.

Indeed it would be criticized by the many of us that find this Ada feature annoying.

Re: Ada.Streams.Stream_IO.File_Type

[Robert I. Eachus]

M�rio Amado Alves wrote:
>>...
>>but it could be implemented by putting:
>>
>>   type File_Type is new Ada.Finalization.Limited_Controlled with private;
>>
>>in the private part of package Ada.Streams.Stream_IO. I'm not quite sure if
>>such an implementation would be criticised on the grounds that objects of
>>File_Type could not then be declared other than at library level.

> Indeed it would be criticized by the many of us that find this Ada feature annoying.

So annoying that if there was such a requirement, I am sure that the ARG 
would immediately eliminate it!

I think that Nick Roberts was thinking of the rule that prevents 
creating a TYPE derived from Ada.Finalization.Limited_Controlled other 
than at the library level from having a record extension RM 3.9.1(3) and 
the note at RM 3.9.1(7).  I would like to loosen that up some in Ada 0Y 
to allow derived types of the form:

     type New_T is new tagged T;

in some nested contexts.  But it is probably not a high priority 
extension.  (Note that the declaration above is not currently 
syntactically legal.)  If it were added, though, the key would be 
insuring that there was no distributed overhead.  That's the hard part.

-- 

                                                        Robert I. Eachus

�In an ally, considerations of house, clan, planet, race are 
insignificant beside two prime questions, which are: 1. Can he shoot? 2. 
Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and 
Steve Miller.

Re: Ada.Streams.Stream_IO.File_Type

[Nick Roberts]

"Robert I. Eachus" <rieachus@attbi.com> wrote in message
news:3F1AA639.5070200@attbi.com...

> I think that Nick Roberts was thinking of the rule that
> prevents creating a TYPE derived from Ada.Finalization
> .Limited_Controlled other than at the library level from
> having a record extension RM 3.9.1(3) and the note at
> RM 3.9.1(7).

I was. Sorry.

--
Nick Roberts

Re: Ada.Streams.Stream_IO.File_Type

[Robert I. Eachus]

Nick Roberts wrote:

> I was. Sorry.

No, problem, I knew what you meant.  But someone agreed with your post, 
so I responded to make sure we didn't get snarked:

"Just the place for a Snark!" the Bellman cried,
As he landed his crew with care;
Supporting each man on the top of the tide
By a finger entwined in his hair.
"Just the place for a Snark! I have said it twice:
That alone should encourage the crew.
Just the place for a Snark! I have said it thrice:
What I tell you three times is true."

-- The Hunting of the Snark: an Agony in Eight Fits by Lewis Carroll

(If you never have read it, or haven't read it in ages, it can be found 
in many locations on line. http://oldpoetry.com/volume/164 has 
illustrations by Mervyn Peake another site is 
http://www.snark.de/carroll/snark/)
-- 

                                                        Robert I. Eachus

�In an ally, considerations of house, clan, planet, race are 
insignificant beside two prime questions, which are: 1. Can he shoot? 2. 
Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and 
Steve Miller.