[Insight-developers] Re: itkSubsample issues

[Brad Davis]

By the way, I did run ctest (cvs version of Insight from yesterday)
and all the tests passed with this change in place (linux x86_64, gcc
4.0.4).

On 8/15/06, Brad Davis <brad.davis at kitware.com> wrote:
> I propose changing the implementation of GetMeasurementVector in the
> Subsample class from
>
> const MeasurementVectorType & GetMeasurementVector(const
> InstanceIdentifier &id) const
> { return m_Sample->GetMeasurementVector(id) ; }
>
> to
>
> const MeasurementVectorType & GetMeasurementVector(const
> InstanceIdentifier &id) const
> { return m_Sample->GetMeasurementVector(m_IdHolder[id]) ; }
>
> First, the current implementation allows access to measurement vectors
> that are not in the subsample---GetMeasurementVector gets vectors from
> the sample, not the subsample.  Second, while the
> GetMeasurementVectorByIndex() method can be used to return the
> measurement vectors that are actually in the sample, the change in
> interface means that it is difficult to write general code that will
> work for a sample or a subsample.  Also, GetMeasurementVectorByIndex
> returs by value rather than by reference.  Iterators can be used but
> using both iterators and GetMeasurementVectorByIndex() it is
> impossible to have a working subsample of a subsample---the
> implementation only allows for one level of indirection.  Again this
> means that you have to know a priori if you are working with a sample
> or subsample.
>
> The change that I propose allows Samples and Subsamples to be
> addressed by a common interface, and allows the programmer to create a
> Subsample of either a Sample or a Subsample.  This would increase the
> flexibility of the classes and allow for more general code.
>
> The drawback of the change is that if someone is already using the
> GetMeasurementVector() method of the Subsample class to directly (and
> incorrectly, I argue) access vectors from the Sample, then the change
> is not backward compatible.  However, access to the Sample can also be
> gained by Subsample's GetSample method.
>
> The other mechanism for fixing this problem is to add a
> GetMeasurementVectorByIndex() method to the Sample class, and change
> the method to return by reference.  This does not require changing the
> GetMeasurementVector method but it makes the classes more confusing.
>
> Brad
>