[Insight-developers] Compile-time decorator pattern

[Luis Ibanez]

Hi Brad,

The name of this pattern is:

         "The Curiously Recurring Template Pattern"

or CRTP for short.

http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern


It is used abundantly in ITK in the Mesh hierarchy and the CellTypes.

See for example the TriangleCell:

template< typename TCellInterface >
class ITK_EXPORT TriangleCell:
  public TCellInterface, private TriangleCellTopology
{


----


It certainly will be interesting to explore it use in the GPU
classes than Won-Ki posted to Gerrit:

   http://review.source.kitware.com/#change,673



    Luis



-----------------------------------------------------------------------------------
On Fri, Jan 7, 2011 at 1:42 PM, Bradley Lowekamp <blowekamp at mail.nih.gov> wrote:
> Hello,
> I have just push a little branch which shows the basis for a potentially
> very useful design pattern for ITK filters:
> http://review.source.kitware.com/#change,684
> I could not find an official name for this patterns, I have read about it
> before and used it in a few places as well in other projects. I decided to
> call it "compile-time decorator" because it's design to add features to a
> multiple class hierarchies.
> The motivation is to be able add reuse functionality, without changing
> exiting hierarchy structures. This an alternative to multiple inheritance in
> for some situations.
>
> The implementation of the pattern is to have the parent of a class be a
> template argument to the class.
> template< class TInputImage, class TOutputImage = TInputImage,
> class TParentImageFilter = ImageToImageFilter< TInputImage, TOutputImage > >
> class ITK_EXPORT InPlaceImageFilter: public TParentImageFilter {...}
>
> For example say I have a good inplace algorithm for WhiteTopHatImageFilter:
> http://www.itk.org/Doxygen/html/classitk_1_1WhiteTopHatImageFilter.html
> However, it's already embedded in an existing complex hierarchy, so I can
> not re-organize the class to be derived from InPlaceFilter. However, it's is
> good practice to reuse the existing code in the InPlace filter. This can be
> over come with this pattern by declaring the class in the following fashion.
> template< class TInputImage, class TOuputImage, class TKernel >
> class ITK_EXPORT WhiteTopHatImageFilter:
> public InPlaceImageFilter<TInputImageFilter, TOutputImageFilter,
> KernelImageFilter< TInputImage, TOutputImage, TKernel > >
> {...}
>
> This may be a useful design pattern for GPU implementations of filters,
> along with adding certain streaming functionality to sinc like filters.
> Brad
>
> ========================================================
>
> Bradley Lowekamp
>
> Lockheed Martin Contractor for
>
> Office of High Performance Computing and Communications
>
> National Library of Medicine
>
> blowekamp at mail.nih.gov
>
>
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