Points and Vectors in 3D

[Caligo]

Given everything that D offers, what would be the best way to implement a
Point and a Vector type?  The same (x, y, z) can be used to represent
vectors, but a point represents a position, whereas a vector represents a
direction.  So, would you define two different structs for each? or define
and implement an interface?  a fixed array or POD members?