Should I convert a class with only methods to free functions in a namespace?

Question

I originally created a class like so:

class A
{
  public:
   void run(int x);

  private:
   void run_helper1();
   void run_helper2();
   void run_helper3();

   int a_;
   double b_;
   bool c_;
};

Later I realized it really didn't need any state, I just needed the functions. Would it make sense to drop the class and make these free functions in a namespace? If so, I lose the concept of public and private and end up with run_helper1(), run_helper2(), run_helper3() all being public, if I'm not mistaken. That seems like a poor design.

Answer 1

The main difference between class and namespace that a class is closed (but possibly extensible using inheritance) and holds an invariant; while a namespace is open and can be extended at any point. Invariant might be as simple as having a unique address (and being able to compare instance addresses), but, if I understand you correctly, even that is unnecessary.

If there's really no other use of A than to 'group together' functions, then your intuition might be right and you might want change it to a namespace.

There is, however, an example what a namespace can't do that a class can: there are no template namespaces. Thus, if you ever need to pass the methods together, e.g. as an API (or a versioned API), then you need to keep them as a class. In that case, callee templates over the whole collection of functions and you can have multiple such collections; but it's a rather rare use-case.

Thus, normally you can convert it.