rpg_svo | Semi-direct Visual Odometry | Robotics library

But can't we just do this const FramePtr frame?

Sure, we could, but then the copy constructor would be invoked, which is for larger types (anything larger than the built-in types) normally more expensive than passing by reference. This is nothing specific to shared_ptr. It should be generally your default to pass any objects by const reference if you don't need a copy and don't want to change them. Only built-in types like int, float, or char should be passed-by-value.

More interesting is why func1 uses a copy. Most probable case is that he needs a copy anyway, because he wants to keep a reference in the class. I couldn't find the exact file you're refering to in the github repository you've posted. If it's still unclear please past the function body of func1 into the question.

Edit: Ah, I see. Looks like the reason he passes-by-value here, has more to do with thread-safety. Didn't read the whole but otherwise the shared_ptr might be deleted by the owning thread if he passed by const reference.

Here for examle func needs pass-by-value cause otherwise the pointer could be deleted by the main thread. Probably something like this but more complicated: