Can I borrow a pointer to a shared trait in Rust? -

from tutorial on borrowed pointers (broken), bit modified:

struct point {x: float, y: float}  fn compute(p1 : &point) {}  fn main() {     let shared_box : @point = @point {x: 5.0, y: 1.0};     compute(shared_box); } 

and fine, because shared box automatically borrowed function.

but doing same trait:

struct point {x: float, y: float} trait tpoint {}  impl tpoint point {}  fn compute(p1 : &tpoint) {}  fn main() {     let shared_box : @tpoint = @point {x: 5.0, y: 1.0} @tpoint;      compute(shared_box);     //      ^~~~~~~ error here } 

and fails, (compiler version 0.6) saying:

error: mismatched types: expected &tpoint found @tpoint (trait storage differs: expected & found @)

is bug in compiler? or borrowed pointers not allowed traits?

if answer latter, why that?

this known bug in current version of rust:

#3794: casting trait doesn't auto-coerce &t type

there has been work on trying address problem, there technical details need ironed out; interested parties can see of discussion (from few months ago) here on pull request 4178.