Question

Let’s say I have a large, between 50 and 200, pool of individual functions whose job it is to operate on a single object and modify it. The pool of functions is selectively put into a single array and arranged in an arbitrary order.

The functions themselves take no arguments outside of the values present within the object it is modifying, and in this way the object’s behavior is determined only by which functions are executed and in what order.

A way I have tentatively used so far is this, which might explain better what my goal is:

class Behavior{
    public:
    virtual void act(Object * obj) = 0;
};

class SpecificBehavior : public Behavior{
    // many classes like this exist
    public:
    void act(Object * obj){ /* do something specific with obj*/ };
};

class Object{
    public:
    std::list<Behavior*> behavior;

    void behave(){
        std::list<Behavior*>::iterator iter = behavior.front();
        while(iter != behavior.end()){
             iter->act(this);
             ++iter;
        };
    };
};

My Question is, what is the most efficient way in C++ of organizing such a pool of functions, in terms of performance and maintainability. This is for some A.I research I am doing, and this methodology is what most closely matches what I am trying to achieve.

edits: The array itself can be changed at any time by any other part of the code not listed here, but it’s guaranteed to never change during the call to behave(). The array it is stored in needs to be able to change and expand to any size

Answer 1

If the behaviour functions have no state and only take one Object argument, then I’d go with a container of function objects:

#include <functional>
#include <vector>

typedef std::function<void(Object &)> BehaveFun;
typedef std::vector<BehaveFun> BehaviourCollection;

class Object {
  BehaviourCollection b;

  void behave() {
    for (auto it = b.cbegin(); it != b.cend(); ++it) *it(*this);
  }
};

Now you just need to load all your functions into the collection.