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From: Michael Erdmann <Michael.Erdmann@snafu.de>
Newsgroups: comp.lang.ada
Subject: Re: Usage of Interfaces with Ada 95
Date: Sat, 27 Sep 2003 17:05:14 +0200
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Date: 2003-09-27T17:05:14+02:00
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Hyman Rosen wrote:

> Michael Erdmann wrote:
>> The point is that in java i am able to provide an interface
>> which is called IIterator and use this interface in different
>> implementation, but it is the same interface which has to be
>> understood by the programmer only once!
> 
> No; what does your iterator return when you ask for the
> next element? An Object, I presume. Then the client must
> cast it to the type he thinks it is. That's a terrible
> interface, and certainly not worth copying.

This is exactly what happens in a lot of java code i have 
seem. They are using somthing like

    if(  x.istanceOf(...) ) {
    }

I feel the same way, this is a stupid aproach which also
leads to stability problems when something changes in the 
environment and new types are introduced.

The consequence is, that i have to stick with the somewhat 
complicated process:

  1. Define a concept as a generic, eg.

     generic
        type aType ....;

     package ... is 

        type Object is abstract ...

        funtion Get(This : Object) return aType is abstract; 
        .. other methods defining the concept
    end package;

  2. Provide a specific application of the concept to a 
     data type to avoid the cast issue.
     (lets call this an specefic interface)

  3. Use the specific interface within an application.

Maybe i need drop my original idea completley. The idea was to 
provide a set of interfaces which are allowing to develop
software based on concepts (patterns). The Enumeration is 
such a concept beside of a lot of other patterns.
My hope was/is to simplyfy code by using standard patterns.


Regards
   M.Erdmann