Do you mean that unordered_map can automatically instantiate a hashing function for any type of pixel? I have tried this: boost::hash() And VC11 will spit: error C2664: 'boost::hash_value' : cannot convert parameter 1 from 'const boost::gil::rgb8_pixel_t' to 'std::type_index' Thanks. 2013/3/26 Christian Henning

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I've been looking for a hashing function for PixelBased types... with no succes, so I created one. Does this have any value for users?

How about the one supplied by unordered_map?

Christian

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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:

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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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