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From: "Samuel T. Harris" <u61783@gsde.hou.us.ray.com>
Newsgroups: comp.lang.ada
Subject: Re: User define attributes
Date: Mon, 16 Apr 2001 09:35:38 -0500
Organization: Raytheon Aerospace Engineering Services
Message-ID: <3ADB033A.F10344A9@gsde.hou.us.ray.com>
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Date: 2001-04-16T09:35:38-05:00
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Martin Dowie wrote:
> 
> well, if you mean someting like
> 
> type My_Type ...;
> for My_Type'Image use ...;
> 
> you can't (that's for stream read/write only... I think), but as
> attributes are defined as functions anyway (check annex L) you can
> force your generic to require an Image function and even do nifty
> instantiations like...
> 
> generic
>   type My_Type is private;
>   with function Image (X : My_Type) return String;
> package Test is
>   procedure Call (X : My_Type);
> end Test;
> 
> with Test;
> package Tester is new test (Integer, Integer'Image);
> 
> For composite types you have to "roll your own" Image routine that
> would probably just call up the scalar 'Image routines in turn
> or other rolled composite IMage routines.
> 

It is trivial to build a generic which implements the a
width, value, and image function for arrays. All it needs
are the width, value, and image functions for the indexes
and composite types.

It is somewhat harder to build a generic for records
since the "index" are the field names and the composite
function depend upon which field is in use. But it
can be done.

I routinely write width, value, and image functions
for all my important types. Having these generics
in place, I get these routines with some simple
handler code and a generic instantiations. With them
I get the following advantages ...

1. I can easily insert put_line kinds of debug code.
2. If supported, I can call them within my debugger.
3. I can defer aggregrate initialization of variables
   to file_io during elaboration, and vice-versa.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"