extract velocity function

note we have to pass a reference to "facing" not the
tuple itself, otherwise it owns it and we get
"value used here after move"

src/main.rs

@@ -8,13 +8,17 @@ mod rover {
 
     type Rover = (i32, i32, Facing);
 
-    pub fn forward((lon, lat, direction) : Rover) -> Rover {
-	let (xoff, yoff) = match direction {
+    fn velocity(direction : &Facing) -> (i32, i32) {
+	match direction {
 	    Facing::N  => ( 0, -1),
 	    Facing::E  => ( 1,  0),
 	    Facing::S  => ( 0,  1),
 	    Facing::W  => (-1,  0)
-	};
+	}
+    }
+
+    pub fn forward((lon, lat, direction) : Rover) -> Rover {
+	let (xoff, yoff) = velocity(&direction);
 	(lon + xoff as i32, lat + yoff as i32, direction)
     }
 }