nn is a type that helps you enforce at compile time the contract that a given pointer
can't be null. It wraps around raw pointers or smart pointers, and works particularly
well out of the box with std::unique_ptr and std::shared_ptr.
Here's an example:
class Widget : public WidgetBase { public: Widget(nn_shared_ptr<Gadget> gadget) : m_gadget(move(gadget)) {} // ... private: nn_shared_ptr<Gadget> m_gadget; }; // nn_make_unique and nn_make_shared always return non-null values nn_unique_ptr<Widget> my_widget = nn_make_unique<Widget>(nn_make_shared<Gadget>()); // but what if we have a pointer already and we don't know if it's null? shared_ptr<Gadget> this_might_be_null = ... my_widget = nn_make_unique<Widget>(NN_CHECK_ASSERT(this_might_be_null)); // implicit nn_unique_ptr -> nn_shared_ptr works just like unique_ptr -> shared_ptr nn_shared_ptr<Widget> shared_widget = move(my_widget); // the `nn` implicitly casts away if needed void save_ownership_somewhere(shared_ptr<Widget>); save_ownership_somewhere(shared_widget); // implicit upcasts work too nn_shared_ptr<WidgetBase> base_ptr = shared_widget;
Compile-time checking helps find bugs sooner. At Dropbox we use nn pervasively in our
cross-platform C++ codebase.
Compatibility
nn is C++11 compatible. Tested with GCC 4.8, clang 3.6+ and MSVS 2015.