[Insight-developers] Returning a smart pointer or a pointer?

[Bill Lorensen]

If we do add a new method, I think it should have a RawPointer suffix.
Pointer is used as a suffix to typedefs of smart pointers.

Also, I just looked in the SymmetricForcesDemonsRegistration class and
it calls the GetDeformationField method frequently. Also, in the
coverage PDEDeformableRegistrationFuntion::GetDefromationField() is
called 79,000,000 times.

http://www.itk.org/Testing/Sites/zion.kitware/Linux-g++-3.4/Coverage/__Code_Algorithms_itkPDEDeformableRegistrationFunction_h.html

Bill

On Mon, May 19, 2008 at 1:35 PM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>
> Hi Tom, Bill, Ken,
>
> Here is a suggestion:
>
>
> 1) Add a new method called
>
>
>      FieldType * GetDeformationFieldPointer()
>
>   or
>
>      FieldType * GetDeformationFieldRawPointer()
>
>  Then track from where in ITK the original method
>  was being called, and replace it with this new
>  one.
>
>
> 2) This may also require to do the same function
>   addition in the base classes of the PDFDeformable
>   RegistrationFunction, and its derived classes,
>   as well as the invocation of that method from
>   all the classes.
>
> This will keep the original method around, and still
> should help to solve the performance issue inside ITK.
>
> Additionally, we should add a comment in the GetDeformationField()
> method, warning users that the use of this method involves a
> performance penalty and the an alternative, faster method,
> is available.
>
>
>   Luis
>
>
> -------------------------
> Tom Vercauteren wrote:
>>
>> Hi all,
>>
>>
>>> The change will affect users that create a subclass and override the
>>> method.
>>
>> This was indeed the backwards compatibility issue I was thinking of. I
>> just cannot really figure why someone would do something like that...
>> But as Bill said, this is unpredictable.
>>
>>
>>
>>>> a) When the object to be returned is a member variable of the
>>>>  class, then a raw pointer is returned, and preferably a
>>>>  "const" raw pointer.
>>>>
>>>>
>>>> b) When the object to be returned is a newly created object,
>>>>  then a SmartPointer is the preferred method, since it will
>>>>  force users of this class to receive the value in a SmartPointer
>>>>  and will prevent the returned object from "death in transit".
>>
>> Ok thanks for the clarification.
>>
>>
>>> How much of a performance hit are you seeing?
>>>
>>> Maybe we will have to define a new method? Are their other classes
>>> that have the same p[problem?
>>
>> I don' remember the exact performance hit. I was at least a few
>> percents since it was appearing on the profiler output. I haven't seen
>> any other problematic methods but haven't looked for it. I just check
>> the one that was appearing on the profiler output.
>>
>>
>>> What this function returns is a handle on an image. I fail to see the
>>> case
>>> where you'd be dereferencing this smart pointer often enough to affect
>>> program performance. If you are, you probably need to be using
>>> itk::ImageRegionIterator, or hoist calls to access methods via smart
>>> pointers outside of inner loops.
>>
>> I understand that, but I am not responsible for the code calling this
>> method. It was somewhere in the demons registration hierarchy.
>>
>> Tom
>>
>