How to make boost::make_shared a friend of my class

Question

I have written a class with protected constructor, so that new instances can only be produced with a static create() function which returns shared_ptr\'s to my class. To provide

Answer 1

I ended up using the below simple solution to enforce shared ownership. No friendship required.

class probe {
    probe() = default;
    probe(...) { ... }

    // Part I of III, private
    struct creation_token {};
    probe(probe const&) = delete;
    probe& operator=(probe const&) = delete;

public:
    // Part II of III, public
    template 
    probe(creation_token&&, Args&&... args):
        probe(std::forward(args)...) {}

    // Part III of III, public
    template 
    static auto create(Args&&... args) {
        return make_shared(creation_token(),
            std::forward(args)...);
    }
};