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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Your wish list for Ada 202X
Date: Wed, 23 Apr 2014 18:27:42 +0200
Organization: cbb software GmbH
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Date: 2014-04-23T18:27:42+02:00
List-Id: <comp.lang.ada>

On Wed, 23 Apr 2014 17:46:04 +0200, J-P. Rosen wrote:

> Le 23/04/2014 16:38, Dmitry A. Kazakov a écrit :
>>> And what is the benefit over writing:
>>> >    Put_Line (F_T2_Image (V2));
>>> > ?
>> generic
>>     type T is private;
>> package Foo is ...
>> 
>> package body Foo is
>>    procedure Bar (X : T) is
>>    begin
>>        ... X'Img ...
>>  
>> That is the only use case for an attribute, in absence of primitive
>> operations of course.
> 
> But that would require every type to have a 'Img. Yes, you said you
> wanted that, but there are clearly types where no sensible image could
> be provided.

No, I didn't want that.

Instead I would do two things:

1. Classes for all types;

2. An interface named Printable (or whatever else name) with the primitive
operation Image.

Now, if a type is supposed to have Image, it must implement the interface.
All scalar types will.

If a record type need to have Image, you inherit to Printable. If Image is
needed in a generic the formal type inherits to Printable. That's it.

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