ServiceAvailability.swift

import UIKit

class Service {
    typealias ServiceId = String
    let id: ServiceId
    
    init(id: ServiceId) {
        self.id = id
    }
}

class ServiceAvailability {
    func checkAvailabilityOf(serviceId: Service.ServiceId, handler: (Service.ServiceId, Bool) -> ()) {
        handler(serviceId, true)
    }
}

let service = Service(id: "myServiceId")

let availability = ServiceAvailability()

availability.checkAvailabilityOf(serviceId: service.id) { id, available in
    print("service \(id) is available? \(available)")
}