Question

This is my first question on this platform. I am sorry if something is unclear or if I failed to ask in an appropriate way.

The code below should compile with any C++11 Compiler. I tried to reduce it to the minimum. The sense of this code might got lost during this procedure, but it should still be clear that I am trying to do keep a list of classes and corresponding member function to call them all with the same parameter:

#include <iostream>

class Base {
public:
  virtual void Call(int x) = 0;
};

template<class T> class Extended : public Base
{
  public:
  // Constructor.
  Extended(T* ptr, void (T::*memberFunction)(int)) : _ptr(ptr), _memberFunction(memberFunction) { }

  // Call function.
  void Call(int x) {
    (_ptr->*_memberFunction)(x);
  }

private:
  // Pointer to class T.
  T* _ptr;

  // Function pointer.
  void (T::*_memberFunction)(int);

};

class Test1 {
public:
  void Fun1(int x) { std::cout << "Hello " << x << std::endl; }
};

class Test2 {
public:
  void FunX(int x) { std::cout << (x * 2) << std::endl; }
};

class MyList {

 public:
 ~MyList() {
    for (auto it = _list.begin(); it != _list.end(); ++it) {
      delete (*it);
    }
  }

  template <class T> void Add(T* t, void (T::*memberFunction)(int)) {
    _list.push_back(new Extended<T>(t, memberFunction));
  }

  void CallAll(int g) {
    for (auto it = _list.begin(); it != _list.end(); ++it) {
        (*it)->Call(g);
    }
  }

private:
  std::list<Base*> _list;
};


int main() {
  MyList myList;
  Test1 test1;
  Test2 test2;
  myList.Add(&test1, &Test1::Fun1);
  myList.Add(&test2, &Test2::FunX);
  myList.CallAll(100);
}

This works perfect. My problem is that I do not know how to remove a class and member function from the list. Furthermore I do not want the same class and member function to be called twice which is virtually the same problem. I need to check two classes of type Base for equality. I could provide a virtual function which gives me a void pointer.

virtual void* GetPtr() = 0;

But that would only check for equality of the class. I have no clue how to check for equality of function pointers of this class and how

template <class T> void MyList::Remove(T* t, void (T::*memberFunction)(int)) {

}

has to look like.

Does someone know the solution to the problem? Or is this check not possible?

Joe

Answer 1

Add virtual isEqual method to Base.

class Base {
public:
  virtual void Call(int x) = 0;
  virtual bool isEqual(const Base& other) = 0;
};

template<class T> class Extended : public Base
{

  public:
      virtual bool isEqual(const Base& other)
      {
         const Extended* otherPtr = dynamic_cast<const Extended*>(&other);
         return otherPtr != nullptr && otherPtr->_ptr == _ptr && otherPtr->_memberFunction == _memberFunction;
      }

};

And add virtual destructor to Base, otherwise you have memory leak,

And do not use undescore at the beginning of member variable _ptr – if you must use at the end: ptr_. Some leading underscores are reserved for compiler.