Generic dispatcher for multiple classes - c++

Question

I am trying to achieve the same effect in C++. In Python it is so simple to just pass a class method pointer to a dispatcher and to execute the function callback when the specific event occurs. The effect I am looking for is a true generic dispatch class method. Also, the classes should not be related in any way (like in the example below).
class Dispatcher:
def __init__(self):
self.map = {}
def register(self, func, event):
try:
self.map[event].append(func)
except KeyError:
self.map[event] = [func]
def dispatch(self, event):
for func in self.map[event]:
func(event)
class A:
def __init__(self):
pass
def foo(self, event):
print("A", event)
class B:
def __init__(self):
pass
def bar(self, event):
print("B", event)
if __name__ == '__main__':
d = Dispatcher()
a = A()
b = B()
d.register(a.foo, 6)
d.register(b.bar, 6)
d.register(a.foo, 7)
d.dispatch(6)
Expected output:
A 6
B 6

Answer 1

#include <map>
#include <vector>
#include <functional>
using namespace std;
class dispatcher
{
public:
using event_t = int;
using callback_t = function<void(event_t)>;
void register(callback_t c, event_t e)
{
m[e].emplace_back(move(c));
}
void dispatch(event_t e)
{
for(auto&&c: m[e])
c(e);
}
private:
map<event_t, vector<callback_t>> m;
};
You can do something like this. I wrote this in one go on mobile so I have no idea if it works.
That said, this won’t really work exactly the same way as you cannot pass functions that automatically capture the thisptr of an object. You’ll use it as follows, with a functor:
A a;
d.register([&](int i){a.foo(i);}, 6);