Only for those sequences whose size is fixed at compile-time, i.e. af::tiny, af::small and any type derived from them, which at the moment is limited to scitbx::vec3 and scitbx::vec2 from the top of my head. If you return an array with a dynamic size, i.e. af::shared or af::versa, then it will be converted to scitbx.array_family.shared and scitbx.array_family.flex respectively.