Boost intrusive pointer
boost, boost-intrusive, c++, pointers, shared-ptr
Solution
You have to provide these functions. This is how `boost::intrusive_ptr` operates.
Let's compare it with `boost::shared_ptr`. `shared_ptr` manages the reference count itself in the control block associated with the pointee. Creating a `shared_ptr` increments the refcount. Destroying a `shared_ptr` decrements the refcount. When the refcount goes to 0, the pointee is destroyed.
`intrusive_ptr` works in exactly the same way, but does not manage the reference count itself. It just signals to its client "now the refcount must be incremented" and "now the refcount must be decremented." It does that by calling the two functions mentioned, `intrusive_ptr_add_ref` and `intrusive_ptr_release`. If you do not define them, you will get a compilation error.
Think of these functions as the interface to the reference counter. Using `intrusive_ptr` indicates that the refcount is managed somewhere outside the pointer (usually in the pointee itself), and the pointer just intrudes on that refcount, using it for its purposes.
Problem
I'm a little confused about boost's intrusive pointer. The definition says: "Every new `intrusive_ptr` instance increments the reference count by using an unqualified call to the function `intrusive_ptr_add_ref`, passing it the pointer as an argument. Similarly, when an `intrusive_ptr` is destroyed, it calls `intrusive_ptr_release`; this function is responsible for destroying the object when its reference count drops to zero. The user is expected to provide suitable definitions of these two functions. " Does this mean that I HAVE TO implement these methods, or that I CAN do it? The point is, that we're using it because a function requires an intrusive pointer. We've used shared pointer the other places, so were just worried if the pointer is managed, and is going to be deleted when theres no more references to it.