[Insight-developers] Template function specialization

[antonin perrot-audet]

Thanks a lot William, I implemented your solution and it works perfectly !

I will now try to pass a pointer to an image of fixed dimension to 
GenerateData, to avoid the construction of the dummy structure.

Yes indeed, I think I was trying to do partial template specialization 
of a member function, which seems to be forbidden in C++ ?

thanks again,

Cheers

On 01/18/2011 06:32 PM, Williams, Norman K wrote:
> The problem you're running into is that C++ is very touchy about templates
> and specialization. It's rather a confusing topic, about which books are
> written.  The solution involves some form of Template Metaprogramming.
>
> Below is one solution to your problem, that I came up with off the top of
> my head. It uses member function overloading, and doesn't require partial
> template specialization, which is what I think you were trying to do.
> There are other ways to do this, but this is the one that came immediately
> to mind:
>
> #include<iostream>
> #include<itkImage.h>
>
> template<class ImageType>
> class TestOverLoad
> {
> public:
>    void GenerateData();
> private:
>    // dummy type to discriminate dimension at compile time
>    template<unsigned dim>  struct DimType {};
>    // the general ND case -- template member function
>    template<unsigned dim>   void GenerateData(DimType<dim>  *);
>    // the 2D special case -- non-template member function
>    void GenerateData(DimType<2>  *);
> };
>
> // The 2D special case
> template<class ImageType>
> void
> TestOverLoad<ImageType>::
> GenerateData(DimType<2>  *)
> {
>    std::cout<<  "TwoD case"<<  std::endl;
> }
>
> // General Case ND
> template<class ImageType>
> template<unsigned dim>
> void
> TestOverLoad<ImageType>::
> GenerateData(DimType<dim>  *)
> {
>    std::cout<<  "General Case, Dim ="
>              <<  ImageType::ImageDimension
>              <<  std::endl;
> }
>
> template<class ImageType>
> void
> TestOverLoad<ImageType>::
> GenerateData()
> {
>    // depending on dimension of ImageType, only one version of
>    // GenerateData will actually be instantiated
>    // The DimType<dim>  * parameter never used, but it's a low-cost way
>    // to force compile-time type discrimination
>    this->GenerateData(static_cast<  DimType<ImageType::ImageDimension>
> *>(0));
> }
>
> int
> main(int argc, char **argv)
> {
>    TestOverLoad<itk::Image<unsigned char,2>  >  x2;
>    x2.GenerateData();
>
>    TestOverLoad<itk::Image<unsigned char,3>  >  x3;
>    x3.GenerateData();
> }
>