Efficient way to pass struct as parameter

[Tim Hsu via Digitalmars-d-learn]

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?