Re: [Boost-users] Problem with simple type extraction

16 Aug 2010

      Hi Nathan,

On Mon, Aug 16, 2010 at 3:15 PM, Nathan Crookston
 wrote:
...
On Mon, Aug 16, 2010 at 12:32 PM, Christian Henning  wrote:
...
It works for me now too. Any idea why that is?
Well, apparently the reference type is declared as const somewhere in
the GIL code (not the referenced pixel, of course).  I tried to find
exactly where the const was added in the code, but I had some trouble
following all the many metafunction instantiations, etc -- there are
quite a few for the declaration given.
I did not think of const since I thought there is
gray1_image_t::view_t::const_reference. Turns out there isn't a
const_reference. And maybe I got fooled by the MSVC debugger which
told me that there is no const in actual type of
gray1_image_t::view_t::reference.
...
I did modify the metafunction slightly to give correct results
regardless of const (and volatile) qualifiers.  Perhaps it would be of
use to you:
//In addition to previous includes
#include 
namespace boost {
namespace gil {
template< typename T >
struct bit_field_type_impl
{
 typedef T type;
};
template< typename BitField, typename ChannelBitSizes,
         typename Layout, bool IsMutable >
struct bit_field_type_impl< bit_aligned_pixel_reference< BitField
                                                      , ChannelBitSizes
                                                      , Layout
                                                      , IsMutable > >
{
 typedef BitField type;
};
template< typename T >
struct bit_field_type
 : bit_field_type_impl {};
} // namespace gil
} // namespace boost
Thanks alot for your code suggestions I'll incorporate them into my code.

Regards,
Christian