Question

how to remove function that bound to member function of this object :

std::vector<std::function<void(int)>> callbacks;

class MyClass {
public:
    MyClass() {
        callbacks.push_back(
            std::bind(&MyClass::myFunc,this,std::placeholders::_1)
        );
    }
    ~MyClass() {
        auto it = std::remove_if( std::begin(callbacks),
                                  std::end(callbacks),
                                  [&](std::function<void(int)>& f) {
                return // <-- this is my question
                       //     true (remove) if f is bound to member function 
                       //     of this
        });
        callbacks.erase(it,std::end(callbacks));
    }
    void myFunc(int param){...}
};

Answer 1

You can’t in the general case without a buttload of extra work. Type erasure clears this information from the object, and std::function does not expose this information directly.

Your specific example may only have one member function that could be the candidate to remove, but what about a class with 5 members that could be stored as callbacks? You’ll need to test for all of them, and it’s also possible to bind member functions using a lambda, which is pretty much undetectable.

Here’s one solution if:

• all callbacks are registered from within MyClass
• the container is amended to store extra information
• you’re willing to do all the extra bookkeeping

std::vector<std::pair<std::function<void(int)>, void*>> callbacks;

class MyClass{
  static unsigned const num_possible_callbacks = 2; // keep updated
  std::array<std::type_info const*, num_possible_callbacks> _infos;
  unsigned _next_info;

  // adds type_info and passes through
  template<class T>
  T const& add_info(T const& bound){
    if(_next_info == num_possible_callbacks)
      throw "oh shi...!"; // something went out of sync
    _infos[_next_info++] = &typeid(T);
    return bound;
  }
public:
  MyClass() : _next_info(0){
    using std::placeholders::_1;
    callbacks.push_back(std::make_pair(
        add_info(std::bind(&MyClass::myFunc, this, _1)),
        (void*)this));
    callbacks.push_back(std::make_pair(
        add_info([this](int i){ return myOtherFunc(i, 0.5); }),
        (void*)this));
  }

  ~MyClass(){
    using std::placeholders::_1;

    callbacks.erase(std::remove_if(callbacks.begin(), callbacks.end(),
        [&](std::pair<std::function<void(int)>, void*> const& p) -> bool{
          if(p.second != (void*)this)
            return false;
          auto const& f = p.first;
          for(unsigned i = 0; i < _infos.size(); ++i)
            if(_infos[i] == &f.target_type())
              return true;
          return false;
        }), callbacks.end());
  }

  void myFunc(int param){ /* ... */ }
  void myOtherFunc(int param1, double param2){ /* ... */ }
};

Live example on Ideone.