I have often encountered classes with the following structure:

class FooAlgorithm {
  public:
    FooAlgorithm(A a, B b);
    void run();
  private:
    A _a;
    B _b;
};

So classes with only one public member function that are also only run once. Is there any advantage in any case over a single free function foo(A a, B b)? The latter option is easier to call, potentially has less header dependencies and also has much less boilerplate in the header.

CodePudding user response：

An object has state that can be set up at object construction time. Then the single member function can be called at a later time, without knowing anything about how the object was set up, and the function can refer to the state that was set up earlier. A standalone function cannot do that. Any state must be passed to it as arguments, or be global/static (global/static data is best avoided for a variety of reasons).

An hands-on example is worth a thousand abstract explanations, so here is an exercise. Consider a simple object:

struct Obj {
   std::array<std::string, 42> attributes;
};

How would you sort a vector of such objects, comparing only the attribute number K (K being a run-time parameter in the range 0..41)? Use std::sort and do not use any global or static data. Note how std::sort compares two objects: it calls a user-provided comparator, and passes it two objects to be compared, but it knows nothing about the parameter K and cannot pass it along to the comparator.

CodePudding user response：

For bigger projects it may be easier to structure your programm using OOP. For a simple program like yours it is easier to use a single function.

CodePudding user response：

Classes introduce a new dynamic to your program -> Better readability, security, moudularity, re-usability.... functions are used to organize code into blocks.