Question

Suppose I have a class called Poem.

class Poem{
   virtual void recite() = 0;
}

And I have hundreds of .cpp and .hpp files which describe a subclass, like the following

class TheRaven : public Poem{
    void recite() { std::cout << "NEVERMORE!" << endl; }
}

And the likes. And in the main function, I’d like to be able to just iterate through every single possible Poem subclasses and call their recite() function. So I made a class:

class PoemRegistry{
    std::map<std::string, Poem*> poems;
    PoemRegistry& getGlobal(); // returns a static global registry
    void register(const std::string& poemname, Poem * thepoem);
};

And then for each poem subclass .cpp file, I put the following.

class TheRavenRegistor{
    TheRavenRegistor(){
        PoemRegistry::getGlobal().register("theraven", new TheRaven());
    }
}
TheRavenRegistor registor();

ninja edit: I put the global class there, forgot about it

Making it easy, I make a shortcut with #define and templates.

Now, the question is, I just heard about the static class initialization fiasco. I suppose this will be immune against it, or is there something I am definitely missing here? Or is there something more elegant that can be used for this purpose?

Answer 1

This is an example for the Singleton design pattern. Don’t use a static global, since the initialisation order is undefined across compilation units.
Instead use something like this:

PoemRegistry& PoemRegistry::getGlobal()
{
  static PoemRegistry theRegistry; // construction guaranteed when first call
  return theRegistry;
} 

Make the getGlobal() method static:

class PoemRegistry
{
public:
  static PoemRegistry& getGlobal();
...