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From: Michael Erdmann <Michael.Erdmann@snafu.de>
Newsgroups: comp.lang.ada
Subject: Re: Q: Refactorizing code because Inheritance and Interfaces
Date: Tue, 21 Oct 2003 21:58:04 +0200
Organization: gnade.sourceforge.net
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Date: 2003-10-21T21:58:04+02:00
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Stephen Leake wrote:

> Michael Erdmann <Michael.Erdmann@snafu.de> writes:
> 
>> In order to line up the implemenation of the XML_Reader with the
>> Abstract_Reader interface i need to rewrite the complete XML_Reader.
>> Is there any way to avoid such situations?
> 
> In general, no. Refactoring is hard work. That's why it's worth doing :).

Well the code i got a result is not realy nice. The result is now:

1. I had to move the type declaration of the XML Reader into the 
   package body.

2. I needed to define my new type as an implementation of the interface
   is wanted to introdcue.

it looks now like this:

   package ... is

      type Object is new  XX.Interface.Object with private;


   private 
      type Object_Data_Type;

      type Object is new XX.Interface.Object with record
             Data : Object_Data_Access := Initialize;
          end record;

   package


   package body is
  
     type XML_Reader_Type is new SAX ...... with..

     procedure Element_Begin( S : in XML_Reader ....)

     type Object_Type is record
        ....
           Reader : XML_Reader_Type ;
        end record;

   end ..;

This was a lot more refactorizing then i expected! I am now afraid
that i have to spend the effort again, again ......


> 
>> In java i would use   constructs as implements  Sax..,Abstract_Reader.
> 
> Ada 200Y will have interface inheritance similar to Java's. But you
> still need to rewrite the implementation, so I don't see that as
> saving much work.
> 
> You can get something similar to interface inheritance in Ada 95 using
> generic mixins. It depends on the details of what you are doing
> exactly what approach to take.
>