C++ implementation

C++/eventemitter.h

@@ -0,0 +1,53 @@
+#include <map>
+#include <list>
+#include <functional>
+
+template <typename EventName, typename... Arguments> class EventEmitter {
+ private:
+  std::map<EventName, std::map<int, std::function<void(Arguments...)>>>
+  events;
+  unsigned long long listenerKey = 0;
+ public:
+  std::function<void()> on(EventName event,
+                           std::function<void(Arguments...)> listener) {
+    auto key = listenerKey;
+    auto unsubscribe = [ =, this ]() {
+      events[event].erase(key);
+    };
+    events[event][key] = listener;
+    listenerKey++;
+    return unsubscribe;
+  }
+  void emit(EventName event, Arguments... args) {
+    if (events.contains(event)) {
+      for (auto listener : events[event]) {
+        listener.second(args...);
+      }
+    }
+  }
+  void clear(EventName event) {
+    events[event].clear();
+  }
+  int count(EventName event) {
+    return events.contains(event) ? events[event].size() : 0;
+  }
+  std::list<std::function<void(Arguments...)>> listeners(EventName event) {
+    std::list<std::function<void(Arguments...)>> result;
+
+    if (events.contains(event))
+      for (auto listener : events[event]) {
+        result.push_back(listener.second);
+      }
+
+    return result;
+  }
+  std::list<EventName> names() {
+    std::list<EventName> result;
+
+    for (auto event : events) {
+      result.push_back(event.first);
+    }
+
+    return result;
+  }
+};

C++/usage.cpp

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+#include "eventemitter.h"
+#include <iostream>
+
+int main() {
+  EventEmitter<std::string> ee;
+  ee.on("event", []() {
+    std::cout << 1;
+  });
+  auto cancel2 = ee.on("event", []() {
+    std::cout << 2;
+  });
+  ee.on("event", []() {
+    std::cout << 3;
+  });
+  std::cout << "Number of existing event names:" <<
+            ee.names().size() << std::endl;
+  std::cout <<
+            "Number of listeners listening to the event using EventEmitter::count:" <<
+            ee.count("event") << std::endl;
+  std::cout <<
+            "Number of listeners listening to the event using EventEmitter::listeners:" <<
+            ee.listeners("event").size() << std::endl;
+  ee.emit("event");
+  std::cout << std::endl;
+  cancel2();
+  ee.emit("event");
+  std::cout << std::endl;
+  ee.clear("event");
+  ee.emit("event");
+
+  EventEmitter<std::string, std::string> eeWithArgs;
+  eeWithArgs.on("event", [](std::string data) {
+    std::cout << data;
+  });
+  eeWithArgs.emit("event", "hello ");
+  eeWithArgs.emit("event", "there");
+}