Callback

• A thin callback class (defaults to 32bytes, but can be as short as 16 bytes).
• You don't need to derive from anything to get called, just specify the global function, assign a lambda or assign a obj + method pointer.
• No heap allocation requested. The lambda is saved inside the callback itself.
• The local storage defaults to 24 bytes, but can be enlarged if required.
• No copy-ctor, no move semantics or destroying the saved lambda.
• Tested under VisualC++ & OSX

---

// Some type of event registration between uint32_t -> callbacks
template< typename TCallbackType >
class TMsgBus {
  std::unordered_multimap< uint32_t, TCallbackType > callbacks;
public:
  void add(uint32_t id, TCallbackType cb) {
    callbacks.insert(std::pair<uint32_t, TCallbackType >(id, cb));
  }
  void on(uint32_t id) {
    auto range = callbacks.equal_range(id);
    auto it = range.first;
    while (it != range.second) {
      it->second(id);
      ++it;
    }
  }
};


void test())
{
  typedef jaba::Callback<void(int)> TCallback;
  CBase b;
  CDerived1 d1;
  CBase* d2 = new CDerived2;
  int id = 100;

  printf("Testing TCallback3 ----------------\n");
  printf("Sizeof TCallback is %zd\n", sizeof(TCallback));

  // ------------------------------------------
  auto lambda1 = [id](int a) {
    printf("Hi from non-captured-params lambda %d, with params %d\n", a, id);
  };

  // ------------------------------------------
  TMsgBus<TCallback> bus;
  {
    bus.add(10, [&b](int x) { b.method1(x); });
    bus.add(10, [&b](int x) { b.method2(x); });
    bus.add(10, [&d1](int x) { d1.method1(x); });
    bus.add(10, lambda1);
    bus.add(10, publicFn);
    bus.add(10, { &b, &CDerived1::method1 });

  }
  bus.on(10);
}