Completion Handlers in Swift

SomeAbstractLayer.swift

import Foundation

typealias someCompletionHandler = (success: Bool) -> ()

class SomeAbstractLayer {

    static let sharedInstance = SomeAbstractLayer()
    
    var subscribers: [someCompletionHandler]
    
    init() {
        self.subscribers = [someCompletionHandler]()
    }
    
    func addHandler(handler: someCompletionHandler) {
        self.subscribers.append(handler)
    }
    
    func fireSubscribersThing() {
        for subscriber in subscribers {
            subscriber(success: false)
        }
    }
}