verbalsaintmars / nn

Non-nullable pointers for C++

nn: Non-nullable pointers for C++

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.