2.7 KiB
Class AnyHashable and AnyHashableValue reference
Description
The class AnyHashable can be used as the event ID type in EventDispatcher and EventQueue, then any hashable types can be used as the event type.
For example,
eventpp::EventQueue<eventpp::AnyHashable, void()> eventQueue;
eventQueue.appendListener(3, []() {}); // listener 1
eventQueue.appendListener(std::string("hello"), []() {}); // listener 2
eventQueue.dispatch(3); // trigger listener 1
eventQueue.dispatch(std::string("hello")); // trigger listener 2
AnyHashableValue is similar to AnyHashable. AnyHashableValue holds the underlying event ID and can be obtained by the users. AnyHashable doesn't hold the underlying event ID for better performance.
Header
AnyHashable
eventpp/utilities/anyhashable.h
AnyHashableValue
eventpp/utilities/anyhashablevalue.h
Details
Any values of hashable types can be converted to AnyHashable implicitly, thus the values can be passed to EventDispatcher or EventQueue as the event type.
A hashable type is a type that can be used with std::hash.
Note: the hash value calculated by std::hash has chances to collide. Two different event IDs with the same hash will be treated as the same ID.
AnyHashable has only one member function,
std::size_t AnyHashable::getHash() const;
The function returns the hash value.
AnyHashableValue supports getHash as well, and another member function,
const std::any & AnyHashableValue::getValue() const;
getValue returns the underlying event ID value in std::any.
Example code for AnyHashableValue,
eventpp::EventQueue<
eventpp::AnyHashableValue,
void(const eventpp::AnyHashableValue & e)
> eventQueue;
eventQueue.appendListener(
3,
[](const eventpp::AnyHashableValue & e) {
assert(std::any_cast<int>(e.getValue()) == 3);
}
);
eventQueue.appendListener(
std::string("hello"),
[](const eventpp::AnyHashableValue & e) {
assert(std::any_cast<std::string>(e.getValue()) == "hello");
}
);
eventQueue.enqueue(3);
eventQueue.process();
eventQueue.dispatch(std::string("hello"));
When to use AnyHashable and AnyHashableValue?
Even though AnyHashable and AnyHashableValue look smart and very flexible, I highly don't encourage you to use them at all because that means the architecture has flaws. You should always prefer to single event type, such as int, or std::string, than mixing them.
If you want to use AnyHashable or AnyHashableValue, don't forget to take into account of the collision created by std::hash, and be sure your event IDs don't collide with each other.
If you find there are good reasons to mix the event types and there are good cases to use AnyHashable and AnyHashableValue, you can let me know.