ChainOfResponsibility.swift

struct Message {
    let from: String
    let to: String
    let subject: String
}

class LocalTransmitter {
    func sendMessage(message: Message) {
        print("Message to \(message.to) sent locally")
    }
}

class RemoteTransMitter {
    func sendMessage(message: Message) {
        print("Message to \(message.to) send remotely")
    }
}

let messages = [
    Message(from: "[email protected]", to: "[email protected]", subject: "Free for lunch"),
    Message(from: "[email protected]", to: "[email protected]", subject: "New Contracts"),
    Message(from: "[email protected]", to: "[email protected]", subject: "All-Hands Meeting")
]
let localT = LocalTransmitter()
let remoteT = RemoteTransMitter()

for message in messages {
    if let index = message.from.rangeOfString("@") {
        if (message.to.hasSuffix(message.from[Range<String.Index>(start: index.startIndex, end: message.from.endIndex)])) {
            localT.sendMessage(message)
        } else {
            remoteT.sendMessage(message)
        }
    } else {
        print("Error: cannot send message to \(message.from)")
    }
}