> That "why" actually has an answer: "because the function might only copy the shared_ptr conditionally, and desire to remain efficient in the no-copy case". Y

> That "why" actually has an answer: "because the function might only copy the shared_ptr conditionally, and desire to remain efficient in the no-copy case". Yeah. This blog post has a few well argued guidelines about passing smart pointers to functions, which covers this case: https://herbsutter.com/2013/06/05/gotw-91-solution-smart-pointer-parameters/ https://herbsutter.com/2013/06/05/gotw-91-solution-smart-poi... > Use a const shared_ptr& as a parameter only if you’re not sure whether or not you’ll take a copy and share ownership; otherwise use widget* instead (or if not nullable, a widget&).