> That equivalent would be ndarray It seems ndarray is conceptually similar to C libraries, it doesn’t have expression templates. When you write r = a * b * c

> That equivalent would be ndarray It seems ndarray is conceptually similar to C libraries, it doesn’t have expression templates. When you write r = a * b * c with ndarray, you allocate, store and then load a temporary array with a * b. When you write r = a * b * c with Eigen, depending on the types it sometimes skips the temporary, and instead computes the complete expression in one shot. For some use cases, the tactic causes substantial performance win. > Box (or Rc/Arc) An array of boxes will cause another pointer chase: first to load the pointer, another one to reach the payload.