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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Text_IO, was: Re: Something I don't understand
Date: Tue, 18 Feb 2014 09:28:14 +0100
Organization: cbb software GmbH
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Date: 2014-02-18T09:28:14+01:00
List-Id: <comp.lang.ada>

On Tue, 18 Feb 2014 08:50:27 +0100, Georg Bauhaus wrote:

> On 17/02/14 21:09, Dmitry A. Kazakov wrote:
>> Actually it is possible to have it statically type safe with some little
>> compiler support.
> 
> What does "little compiler support" mean?

Binding (and checking) terms of the format expression against the types of
values:

   Put
   (  "Index=" & I (Field=>8, Align=>Right) & "X=" & F (10.2),
      (Index, X)
   );

Here I, integer format, must match Index, F, real format must match X.

>> Ada's style of independent Put and Get is so much better.
>> Note that even C++ switched to this style, I mean its out<< and in>>
>> operators.
> 
> C++, however, has automatic template resolution, Ada hasn't.
> Nor does Ada have anything more fancy than ordinary types,
> no type parameters of types directly, etc.

You would need ad-hoc tuples for handling lists of assorted values to
print, as I used in the example above.

Or else you can use aspects which are so messy anyway that whatever harm to
Ada's syntax it would do, it is already done:

   Put (File) with
      Format => ...,
      Value1 => ...,
      ...
      ValueN => ...;

>The Spitbol operators
> all return Pattern, and they do so for operands of type Pattern,
> character stuff, or function pointers only. No MD.

Yes. I prefer a MD solution and no formats at all.
 
> So, I guess we cannot even have C++-like operator<< etc,
> without a "little compiler support"?

But << operators is an MD solution!

I was talking about a formats. Formats is a poor-man's dispatch. Instead of
using the type information from the value, the format specifies the type
explicitly, e.g. %d, reads among other "integer". That introduces nothing
but yet another source of errors. Also when pursued honestly as FORTRAN and
PL did it requires a whole mess of means for formatting arrays (remember
that horror?) and for a modern OO language records, record extensions etc.
Good luck with that.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de