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Newsgroups: comp.lang.ada
Subject: Re: Idiom for a class and an object in Ada
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From: Matthew Heaney <matthewjheaney@earthlink.net>
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Date: Tue, 19 Oct 2004 03:28:19 GMT
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Jeffrey Carter <spam@spam.com> writes:

> Marius Amado Alves wrote:
> 
> > generic
> >    Line : Number;
> > package AD_Converter is
> >    function OK return Boolean;
> >    function Get return Value;
> > end;
> > package Heat is new AD_Converter (123);
> > package Noise is new AD_Converter (456);
> > package Wind is new AD_Converter (789);
> > -- You can't get more "static" than that!
> 
> Or simple. Or Ada-like. The other suggestions look too much like C++
> for my taste.


Too much code bloat.  There's no reason AD_Converter needs to be a
generic, if the objects of that type are known apriori:

package AD_Converters is
   pragma Elaborate_Body;

   type AD_Converter (<>) is limited private;

   function OK (Converter : AD_Converter) return Boolean;
   function Get (Converter : AD_Converter) return Value;

   function Heat return AD_Converter;
   function Noise return AD_Converter;
   function Wind return AD_Converter;

private

   type AD_Converter (Line : Number) is limited record ...;

end AD_Converters;


package body AD_Converters is
   ...

   Heat_ADC  : AD_Conveter (123);
   Noise_ADC : AD_Converter (456);
   Wind_ADC  : AD_Converter (789);

   function Heat return AD_Converter is
   begin
      return Heat_ADC;
   end;

   function Noise return AD_Converter is
   begin
      return Noise_ADC;
   end;

   function Wind return AD_Converter is
   begin
      return Wind_ADC;
   end;

end AD_Converters;


Alternatively, you could declare the objects each in their own private package:

function AD_Converters.Heat return AD_Converter;

private package AD_Converters.Heat_AD_Converters is
   Heat_AD_Converter : AD_Converter (123);
   ... -- whatever else
end;

with AD_Converters.Heat_AD_Converters;
function AD_Converters.Heat return AD_Converter is
begin
   return AD_Converters.Heat_AD_Converter;
end;


This would be useful if each AD_Converter object had distinct library
dependencies.  (Although it might not matter that much anyway, since
such dependencies would have been limited to the body.)