[Insight-users] Why classes attributes should be private in ITK?

[Luis Ibanez]

Hi Yann,

Thanks for specifying what class and member
variables you needed access to.

Protected Get/Set methods were added for the
NeighborhoodRadius, and a protected Get method
was added for the RealValued image.

You will just need to update your CVS checkout.

Please let us know if this works for the
derivation that you are implementing, or if
you need access to any other internal variables.


BTW,
Could you describe your motivations for
implementing a variant of this filter ?


Would you be willing to contribute your
filter to ITK ?


   Regards,


     Luis


-----------------
Lemeur Yann wrote:

>       Hi,
> Thanks for your answers!
> I'm going to precise my problem: I've made a new classe which inherit from itkVectorGradientMagnitudeImageFilter. My goal was to overload the method ThreadedGenerateData() in order to include a short process on the output pixels (to be more precise:  change unwanted values of gradient). For more performance, I want to include the operation directly in the while loop of ThreadedGenerateData(). But as you can see, this method needs to access to "m_NeighborhoodRadius" and "m_RealValuedInputImage" which are private variables of itkVectorGradientMagnitudeImageFilter without accessors. So I can't use inheritance in this case!
> 
> My conclusion is that such methods (which need access to private data without accessors) become useless for inheritance mechanism. I even think that we could declare them private because we can't overload them!
> Drinking litres of Colombian coffee doesn't conduct me to a solution so I think there is not...
> To my mind, this case is one where private variables aren't very nice.
> Is it a good reason to add Set/Get methods to this class in future versions? (even if I would prefer to have protected variables to avoid changing the parts of code I don't want to change)
> 
> Thanks
> 
> Yann  
> 
> 
>>----------
>>De : 	Luis Ibanez[SMTP:luis.ibanez at kitware.com]
>>Date :	mercredi 14 avril 2004 18:28
>>A :	Lemeur Yann
>>Cc :	insight-users at itk.org
>>Objet :	Re: [Insight-users] Why classes attributes should be private in ITK?
>>
>>
>>Hi Yann,
>>
>>Mmm, You should actually we wondering why
>>there shoule be *any* public or protected
>>variables in ITK classes...
>>
>>Encapsulation is a fundamental principle in
>>Object Oriented programming. Every variable
>>must be private until you prove that the design
>>requires otherwise.
>>
>>Note that for getting access to the variables
>>most ITK classes offer Set() / Get() methods
>>that are constructed with the itkSetMacro and
>>itkGetMacro.
>>
>>Your derived classes should simply use these
>>Get/Set methods for getting access to such
>>variables.
>>
>>If you indicate what classes in ITK are giving
>>you trouble, and what kind of variation of the
>>filters you want to implement, we will be happy
>>to add the Set/Get methods needed for your class
>>to work correctly. That's the beauty of Open
>>Source and Exterme Programming    :-)
>>
>>
>>Please let us know,
>>
>>
>>    Thanks
>>
>>
>>      Luis
>>
>>
>>
>>------------------
>>Lemeur Yann wrote:
>>
>>
>>>Hi everybody!
>>>
>>>I've used ITK for about a month and I wonder why almost all classes variables are private. 
>>>Actually, I have a problem when I want to create a class (class B) which inherit from a mother-class (called class A) in order to change one method (in my case: adding some lines of code to GenerateData() ).
>>>If this method needs to access to class variables which are private (defined in class A), I can't reimplement it in my new class B because variables are private in the mother class A.
>>>I also can't redefine the variables of A with the same name in B! 
>>>
>>>The only solution I've found is to write a "sister class" which inherit from the same class as A, and which is the same as A excepted the few changes I want to add.
>>>Does somebody know another solution to make it properly (ie to avoid to rewrite classes which don't change!)
>>>And I also wonder what is the interest to declare all the class variables private?
>>>
>>>Thanks!
>>>Yann   
>>>_______________________________________________
>>>Insight-users mailing list
>>>Insight-users at itk.org
>>>http://www.itk.org/mailman/listinfo/insight-users
>>>
>>
>>
>>
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