Re: [boost] [gil] Pixel Hasher

26 Mar 2013

      Ok, I guess you solution is better for it uses "static_for_each" which
would turn into statically generated code.
But we may skip pushing stuff into a vector by doing

std::size_t hash = 0;
static_for_each( p, [&] ( const channel_t& c )
        {
           boost::hash_combine(hash, c);
        });

return hash;

Do we agree with this?
Regards.

2013/3/26 Christian Henning 
...
On Tue, Mar 26, 2013 at 9:51 AM, Harg Tholan  wrote:
...
Do you mean that unordered_map can automatically instantiate a hashing
function for any type of pixel? I have tried this:
Ok, I see I was wrong. I simple solution is provided here:
http://stackoverflow.com/questions/10405030/c-unordered-map-fail-when-used-w...
Taking that you can create the following:
template< typename Pixel >
struct pixel_hasher
{
    std::size_t operator()( const Pixel& p ) const
    {
        typedef channel_type<Pixel>::type channel_t;
vector v;
        static_for_each( p, [&] ( const channel_t& c )
        {
            v.push_back( c );
        });
return boost::hash_range( v.begin(), v.end() );
    }
};
typedef rgb8_pixel_t pixel_t;
    pixel_t p( 1,2,3);
    unordered_map< pixel_t, int, pixel_hasher< pixel_t > > n;
    n[p] = 99;
Hope this helps.
Christian
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