Notification+TypedName.swift

import Foundation

extension Notification {
    struct TypedName<Value> {
        let rawValue: String
        
        init(_ rawValue: String) {
            self.rawValue = rawValue
        }
        
        var notificationName: Name {
            return Name(rawValue)
        }
    }
}

private let userInfoKey = "notificationPayloadUserInfoKey"

extension NotificationCenter {
    func addObserver<Value>(
        forName name: Notification.TypedName<Value>,
        object: Any? = nil,
        queue: OperationQueue? = nil,
        using block: @escaping (Value) -> Void
    ) -> NSObjectProtocol {
        return addObserver(forName: name.notificationName, object: object, queue: queue) { notification in
            let value = notification.userInfo![userInfoKey] as! Value
            block(value)
        }
    }
    
    func post<Value>(_ value: Value, name: Notification.TypedName<Value>, object: Any? = nil) {
        self.post(name: name.notificationName, object: object, userInfo: [userInfoKey: value])
    }
}

// Example:

extension Notification.TypedName {
    static var notificationName: Notification.TypedName<Int> {
        return .init("notificationName")
    }
}

NotificationCenter.default.addObserver(forName: .notificationName) { int in
    // ...
}

NotificationCenter.default.post(123, name: .notificationName)