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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: Conditional compilation in Ada?
Date: Thu, 18 Nov 2004 19:03:33 +0100
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Date: 2004-11-18T19:03:33+01:00
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Jeffrey Carter wrote:
> Steve wrote:
> 
>> Using variant records means explicitly checking for the variant type and
>> taking different action based on the variant.  Creating a new 
>> variation of
>> the record means modifying the original record (modifying proven code is
>> never a good thing when it is easily avoided) and chasing each part of 
>> the
>> code that takes different action based on the variants.
> 
> 
> Since the compiler points out any place where you've forgotten, this is 
> hardly a problem; indeed, I would claim that it's an advantage over OOP, 
> where forgetting to redefine an operation is ignored by the compiler, 
> and you get the wrong action instead.
> 
> In a well designed system, all the code dealing with the variant record 
> and its variants will be together, so there's no "chasing each part of 
> the code".
> 
> Another advantage of using a variant record is that what happens is 
> explicit in the code, not hidden is some package that is not mentioned 
> in a context clause.
> 
>> Using objects means deriving a new object and overloading specific
>> operations for that object.  The base object isn't touched.
> 
> 
> And operations that are mistakenly not overridden become run-time errors.

Not if they're declared abstract. Then you have the same situation as 
missing cases for a variant record. Plus you don't have an escape like 
using "when others".

> 
>> Also: If the object is declared statically, the dispatching may happen
>> statically.
> 
> 
> This is true, but it seems that the nature of OP's problem would prevent 
> this.
>