Can you explain the main ways to implement the Responder Chain pattern?

The Responder Chain pattern is used to pass events or requests through a chain of objects until one of them handles the event.

Main implementation methods:

1. Chain through references to the next object — each object contains a reference to the next handler. If the current one cannot handle the event, it passes it further.

2. Using delegates or protocols — an object calls a delegate method, which can pass the event further.

3. In iOS (UIKit) — UIResponder implements the event handling chain. For example, touch events are passed from UIView to its superview, then to the controller, and so on.

Example in Swift:

class Handler {
    var next: Handler?
    func handle(request: String) {
        if canHandle(request) {
            print("Handled: \(request)")
        } else {
            next?.handle(request: request)
        }
    }
    func canHandle(_ request: String) -> Bool {
        return false
    }
}

class ConcreteHandlerA: Handler {
    override func canHandle(_ request: String) -> Bool {
        return request == "A"
    }
}

class ConcreteHandlerB: Handler {
    override func canHandle(_ request: String) -> Bool {
        return request == "B"
    }
}

let handlerA = ConcreteHandlerA()
let handlerB = ConcreteHandlerB()
handlerA.next = handlerB
handlerA.handle(request: "B") // Handled: B

Thus, the Responder Chain allows flexible hierarchical event handling without tight coupling between sender and receiver.