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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Seeking for papers about tagged types vs access to subprograms
Date: Sun, 12 May 2013 17:26:34 -0700
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Date: 2013-05-12T17:26:34-07:00
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On 05/12/2013 03:15 PM, Robert A Duff wrote:
> Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> writes:
>
>> I'm not sure I see the point in having an object for a closed file,
>
> Yeah, I was about to post basically the same thing.  A closed file
> is pretty useless.  It's like an uninitialized variable -- you can't
> do anything with it.
>
>> other than the requirements of low-level languages in which such things
>> were 1st implemented.
>
> Low-level languages like Ada 83?  ;-)

Or even Ada 80 :) But I suspect everything goes back to how files were handled 
in 1950's assembly languages.

> Yes, but I would have separate types for Input_File and Output_File.
> Possibly another type for the rare case when you want to
> read and write to/from the same file handle.

Yes, that's an additional possible refinement.

> But you couldn't use it like this:
>
>      File : File_Info; -- Illegal!
>      ... -- some code that computes File_Name
>      File := Open (File_Name); -- Illegal!
>
> which is a limitation, compared to the current design of Text_IO
> and friends.

That's what block statements are for.

-- 
Jeff Carter
"I fart in your general direction."
Monty Python & the Holy Grail
05