Question

All,

I recently posted this question on DAL design. From that it would seem that passing a reference to an object into a function, with the function then populating that object, would be a good interface for a C++ Data Access Layer, e.g.

  bool DAL::loadCar(int id, Car& car) {} 

I’m now wondering if using a reference to a boost::shared_ptr would be better, e.g.

  bool DAL::loadCar(int id, boost::shared_ptr<Car> &car)

Any thoughts? Does one offer advantages over the other?

What would be the implications of applying const correctness to both calls?

Thanks in advance.

Answer 1

As sbi says, “It depends on what the function does. “

However, I think the most important aspect of the above is not whether NULL is allowed or not, but whether the function stores a pointer to the object for later use. If the function just fills in some data then I would use reference for the following reasons:

• the function can still be used by clients who do not use shared_ptr, used for stack objects, etc.
• using the function with shared_ptr is still trivial – shared_ptr has dereferencing operator that returns a reference
• passing NULL is not possible
• less typing
• I don’t like using “stuff” when I don’t have to

If the function needs to store pointer for later use or you anticipate the function might change in such a way that will require storing a pointer, then use shared_ptr.