Created
March 4, 2022 15:14
Multiple Observer handling by using single observer bridge
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#include <functional> | |
#include <iostream> | |
#include <string> | |
#include <tuple> | |
#include <type_traits> | |
struct IObserver { | |
virtual ~IObserver() = default; | |
virtual void OnMessage(const std::string&) = 0; | |
}; | |
class Publisher { | |
private: | |
IObserver* observer{nullptr}; | |
public: | |
void RegisterObserver(IObserver* observer_) { observer = observer_; } | |
void PublishMessage(std::string msg) { | |
if (observer) { | |
observer->OnMessage(msg); | |
} | |
} | |
}; | |
class ObserverX : public IObserver { | |
public: | |
void OnMessage(const std::string& msg) override { | |
std::cout << "ObserverX::OnMessage: " << msg << "\n"; | |
} | |
}; | |
class ObserverY : public IObserver { | |
public: | |
void OnMessage(const std::string& msg) override { | |
std::cout << "ObserverY::OnMessage: " << msg << "\n"; | |
} | |
}; | |
class ObserverZ : public IObserver { | |
public: | |
void OnMessage(const std::string& msg) override { | |
std::cout << "ObserverZ::OnMessage: " << msg << "\n"; | |
} | |
}; | |
template <typename I, typename... Observers> | |
class MultipleObserverAdapter : public I { | |
private: | |
static_assert(std::conjunction_v<std::is_base_of<I, Observers>...>, | |
"all observer classes should derived from I type"); | |
std::tuple<std::add_pointer_t<Observers>...> observers; | |
public: | |
explicit MultipleObserverAdapter(std::add_pointer_t<Observers>... obs) { | |
observers = std::make_tuple(obs...); | |
} | |
~MultipleObserverAdapter() = default; | |
template <typename Func, typename... Args> | |
void notify(Func&& func, Args&&... args) noexcept(true) { | |
std::apply( | |
[&](auto... obs_pointers) { | |
((obs_pointers->*func)(std::forward<Args>(args)...), ...); | |
}, | |
observers); | |
} | |
}; | |
template <typename... Observers> | |
class MultiObserverBridge | |
: public MultipleObserverAdapter<IObserver, Observers...> { | |
using BaseT = MultipleObserverAdapter<IObserver, Observers...>; | |
public: | |
MultiObserverBridge(std::add_pointer_t<Observers>... observers) | |
: BaseT(observers...) {} | |
~MultiObserverBridge() {} | |
void OnMessage(const std::string& msg) override { | |
BaseT::notify(&IObserver::OnMessage, std::cref(msg)); | |
} | |
}; | |
using ObserversXYZ = MultiObserverBridge<ObserverX, ObserverY, ObserverZ>; | |
int main(int argc, char* argv[]) { | |
Publisher pub; | |
pub.RegisterObserver( | |
new ObserversXYZ(new ObserverX, new ObserverY, new ObserverZ)); | |
pub.PublishMessage("it works!"); | |
return 0; | |
} |
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