C++ Library & Self registering classes: Factory map empty in client application

Question

Let there be a C++ library (let\'s call it lib) which gets included as a static library in an application (let\'s call it app). Within the li

Answer 1

From the blog post, you are missing the static member registered (also called "// The really fun part"). Having and instantiating such a static variable in the base class forces it to be instantiated in all derived classes and this will register the class as a side effect.

EDIT: There is another very small but very important piece of code in the blog post:

    Registrar() : Base(Key{}) { (void)registered; }

This will ensure that registered is used. Because a static variable is only instantiated the first time it is used, otherwise the function is not called.

In your case, adding the following to node_template should work:

template 
struct node_template :
    node,
    factory::registrar
{
    node_template(const std::string& uuid_string) :
        node(uuid_string),
        factory::registrar(uuid_string)
    {
        (void) registered;
    }

    static bool do_register() {
        derived d; // I am not sure if one should in some way force this to not be optimized away.
        return true;
    }

    inline static bool registered = do_register();
};