C++ way of C# Action += function?

Question

in C# we can say:

Action act = ()=> {/*stuff*/}; 
act += ()=> {/*another stuff*/}` 

and then call act().

I wonder how to do such thing in C++ (now with lambdas it will be quite usefull and if possible not using Boost/Qt signals)?

Answer 1

You can write something like this rather easily, by filling a std::vector<std::function<void()>> with the lambdas and invoke every function object.

#include <vector>
#include <functional>
#include <utility>

// warning: very crude and likely with typos / bugs
template<class Sig>
struct Action{
  template<typename Functor>
  void operator+=(Functor&& f)
  { _funcs.emplace_back(std::forward<Functor>(f)); }
  template<class... Args>
  void operator()(Args&&... args) const{
    for(auto& f : _funcs)
      f(args...);
  }
private:
  std::vector<std::function<Sig>> _funcs;
};

// ...
Action<void()> act;
act += []{ /*...*/ };
act += []{ /*...*/ };
act(); // invoke all handlers in order

However, from what I know, C# also allows you to remove a handler with -=, which isn't as easy to accomplish in C++. You'd need to return a token from += which can be passed to -= to remove that specific handler.