Efficient way to pass struct as parameter

[Tim Hsu]

I am creating Vector3 structure. I use struct to avoid GC. 
However, struct will be copied when passed as parameter to 
function


struct Ray {
     Vector3f origin;
     Vector3f dir;

     @nogc @system
     this(Vector3f *origin, Vector3f *dir) {
         this.origin = *origin;
         this.dir = *dir;
     }
}

How can I pass struct more efficiently?