The class Kernel_traits<T> provides access to the kernel model to which the argument type T belongs. (Provided T belongs to some kernel model.) The default implementation assumes there is a local type T::Kernel referring to the kernel model of T. If this type does not exist, a specialization of Kernel_traits<T> can be used to provide the desired information.

This class is, for example, useful in the following context. Assume you want to write a generic function that accepts two points p and q as argument and constructs the line segment between p and q. In order to specify the return type of this function, you need to know what is the segment type corresponding to the Point type representing p and q. Using Kernel_traits<T>, this can be done as follows.

template < class Point >
typename Kernel_traits<Point>::Kernel::Segment
construct_segment(Point p, Point q)
{ ... } 


typedef T::Kernel Kernel; If T is a type K::Point_2 of some kernel model K, then Kernel is equal to K.