What's the right way for doing this in D?

[Namespace]

I liked to know which of this two methods is more common to you, 
A or B:

Method A:
----
import std.stdio;

struct Vector2f {
public:
	float x;
	float y;

	float dot(ref const Vector2f vec) const {
		return this.x * vec.x + this.y * vec.y;
	}
}
----

Method B:
----
struct Vector2f {
public:
	float x;
	float y;
}

float dot(ref const Vector2f lhs, ref const Vector2f rhs) {
	return lhs.x * rhs.x + lhs.y * rhs.y;
}
----

Until now I used Method A, but because of UFCS and the fact, that 
the dot product doesn't affect the object, I thought about which 
way would make more sense. I still like Method A but I'm curious 
what you think.