[Insight-users] OT: Generic Programming - Typedefs inside template functions

[Peter Cech]

On Sun, Jan 07, 2007 at 21:02:41 -0300, Wagner Sales wrote:
> Dears,
> 
> May be that's a fool question, but I'm not so familiar with templates and my searches are returned not useful.
> 
> Well, I'm trying to give some type at a template function and use them to define the image type. My method are:
> 
> template <typename T>
> void MyFilter::processImage(T)
> {
>     if(!m_ImageData) return;
>     // defines the type
>     typedef T PixelType;
>     typedef itk::Image<T, 3> ImageData;
>     ImageData::Pointer m_Image = ImageData::New();

You have to use typename:

      typename ImageData::Pointer m_Image = ImageData::New();

This is because ImageData is derived from a template parameter of the
method (or a class that method is a member of). Whenever you want to use
a typedef from inside of such type, you have to explicitly tell the
compiler it is a type ("typename DerivedType::TypedefedType"). Without
"typename" compiler is treating the construct as a member variable.

>     typedef itk::ImageToVTKImageFilter< ImageData > ToVTKConverter;
>         typedef itk::VTKImageToImageFilter< ImageData > ToITKConverter;
>     typedef itk::BinaryThresholdImageFilter<ImageData, ImageData> FilterType;
>     ToVTKConverter::Pointer m_toVTKConverter = ToVTKConverter::New();

      typename ToVTKConverter::Pointer m_toVTKConverter = ToVTKConverter::New();

>         ToITKConverter::Pointer m_toITKConverter = ToITKConverter::New();

          typename ToITKConverter::Pointer m_toITKConverter = ToITKConverter::New();

>     FilterType::Pointer m_Filter = FilterType::New();

      typename FilterType::Pointer m_Filter = FilterType::New();

> .
> .
> and so on...

and so on...

Regards,
Peter Cech