On Fri, Oct 23, 2009 at 11:27 AM, joel <joel.falcou@lri.fr> wrote:
Emil Dotchevski wrote:
Oh from this point of view yes, the library does allow you to get a vector out of a given column or row of a matrix, you just go m|col<2> and you get a vector type (without actually creating a temporary.)
What's the trick behind that ?
The op| overload takes m by reference, and returns the same reference reinterpret_casted to reference to an instance of this template: template <int Col,class OriginalMatrix> class col_; //non-copyable Then there is this partial specialization of the vector_traits template: template <int Col,class OriginalMatrix> struct vector_traits< col_<Col,OriginalMatrix> > { ... }; The element access functions in that specialization reinterpret_cast the col_<> reference they get back to OriginalMatrix reference and then forward the call to the access functions found in matrix_traits<OriginalMatrix>. There is a bunch of such op| overloads in (Boost) LA, and I wouldn't be shy about adding more: http://www.revergestudios.com/boost-la/view_proxy.html. Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode