Method invocation -- why it's not working?

[Comrad]

   1 struct A
   2 {
   3   double[2] _x;
   4 }
   5
   6 @property ref double y(ref A a) {return a._x[1];}
   7
   8 void main()
   9 {
  10   A a1;
  11   a1.y=2.;
  12 }

dmd test.d gives me:

Error: no property 'y' for type 'A'