Passing const shared_ptr& versus just shared_ptr as parameter

Question

I\'ve been reading quite a number of discussions about performance issues when smart pointers are involved in an application. One of the frequent recommendations is to pass a sm

Answer 1

First of all there is a semantic difference between the two: passing shared pointer by value indicates your function is going to take its part of the underlying object ownership. Passing shared_ptr as const reference does not indicate any intent on top of just passing the underlying object by const reference (or raw pointer) apart from inforcing users of this function to use shared_ptr. So mostly rubbish.

Comparing performance implications of those is irrelevant as long as they are semantically different.

from https://herbsutter.com/2013/06/05/gotw-91-solution-smart-pointer-parameters/

Don’t pass a smart pointer as a function parameter unless you want to use or manipulate the smart pointer itself, such as to share or transfer ownership.

and this time I totally agree with Herb :)

And another quote from the same, which answers the question more directly

Guideline: Use a non-const shared_ptr& parameter only to modify the shared_ptr. 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 * instead (or if not nullable, a &)