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'