Hi Fabien, On Thu, Aug 5, 2010 at 11:02 AM, <fabien.castan@free.fr> wrote:

Hi,

Yes, it works fine without const. I used const automatically because I don't write in my image but I don't think it changes something. So without seems to be better because it's not the correct way to deal with const inside gil.

I would argue that there is a bug in gil since const_view doesn't work with kth_channel_view_type. Maybe we need to have const_kth_channel_view_type or something?

I don't know how we can declare a parameter to be a const view... For example a simple function that takes an image v and returns if it contains a pixel p:

template<class MyGilConstView> bool f( const MyGilConstView& v, const MyGilConstView::value_type& p );

This function can't garantee that it doesn't modify the image v and the pixel p.

The following gives me a compiler error, as expected. template< typename ConstView > void foo( ConstView v ) { typedef typename ConstView::value_type pixel_t; *v.at( 0, 0 ) = pixel_t(); } int _tmain(int argc, _TCHAR* argv[]) { rgb8_image_t img; foo( const_view( img ) ); return 0; } The thing is that you cannot guarantee ConstView to be a const_view, meaning rgb8c_view_t, or etc... . Using concepts would help here, I think.

I can create a const view at the begining of the function, to get this garantee, like this: typedef MyGilConstView::const_t MyGilReallyConstView; typedef MyGilReallyConstView::value_type MyGilReallyConstPixel; // as there is no const_t typedef in pixel type... MyGilReallyConstView cv = v; MyGilReallyConstPixel cp = p;

Is it correct ? Is there a better way to do it ?

I concepts would help. I don't have a better idea right now other than that you and I have to be very careful when passing const_views as a template parameter.

Regards, Fabien

PS: maybe a "typedef value_type pixel_t" inside the view class can be a good thing for readability ?

I believe the name value_type comes from STL. I would prefer pixel_t myself, as well. Regards, Christian