Yuval Ronen wrote:
Is there a common sense about how a shared_ptr<> should be passed to functions/methods: by-value or by-(const-)reference?
1) void test(boost::shared_ptr<A> a); 2) void test(boost::shared_ptr<A>& const a);
You should pass by value. Passing a shared_ptr means giving the opportunity to the callee to use the data without worrying about its lifetime. Would you pass it by ref, the callee won't own the the pointee and hence cannot use it reliabily (it may get deleted behind its back). By passing it by value, the callee makes a copy of the shared_ptr, hence incrementing the ref count. The pointer won't get deleted while the callee use the pointer. Hope it makes sense.
I'm not 100% sure that such a scenario (the pointer gets deleted behind its back if the shared_ptr is passed by ref) is technically possible, but I agree that logically it's better to pass by value.
It is possible. In a multithreaded program, another thread may reset() a. In a single-threaded program, a function called by test() may reset a. I have encountered it myself. If these cases are not a concern, pass by const ref is usually slightly more efficient.