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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
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Subject: Re:
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Date: Wed, 1 Feb 2012 09:49:47 +0100
Organization: cbb software GmbH
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Date: 2012-02-01T09:49:47+01:00
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On Tue, 31 Jan 2012 23:12:57 +0100, Yannick Duch�ne (Hibou57) wrote:

> Le Tue, 31 Jan 2012 18:28:54 +0100, Dmitry A. Kazakov  
> <mailbox@dmitry-kazakov.de> a �crit:
> 
>> On Tue, 31 Jan 2012 00:11:43 +0100, Yannick Duch�ne (Hibou57) wrote:
>>
>>>     type Parsed_Type (Status : Parsed_Status_Type) is record
>>>        case Status is
>>>           when Parsed =>
>>>              Instance : Instance_Type;
>>>           when Format_Error =>
>>>              null;
>>>        end case;
>>>     end record; -- Parsed_Type
>>>
>>>     function Parsed (S : String) return Parsed_Type
>>>        with Post =>
>>>          (if S'Length not in Image_Length_Type then
>>>              Parsed'Result.Status = Format_Error);
>>>           -- There may be other failure conditions.
>>
>> Returning the discussion from the astral spheres back to the topic. A
>> better design could be to split Format_Error into Length_Error and other
>> errors. Then for Parsed the postcondition would become complete for one
>> case: if and only if S'Length not in Image_Length_Type then the result is
>> Length_Error.
> 
> Could be an idea if the program could make use of this extra information.  
> But it won't, a program won't fix an erroneous image received as input,  
> and a Length_Error will result in the same behavior as with a Format_Error  
> result.

What is the point in exempting it in the postcondition? The Georg's idea:
do what looks simple enough and ignore the rest, maybe nobody would ask for
that?

I argue that this attitude is characteristic to bad design. Apart from
thousands other reasons, like leaking implementation details/faults into
the specification etc.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de