 
     class TaskAlreadyExist: ConstraintError {}
 
-    override func schedule(queue: SwiftQueue, operation: SwiftQueueJob) throws {
+    func schedule(queue: SwiftQueue, operation: SwiftQueueJob) throws {
         let exist = queue.operations.contains {
             if let op = $0 as? SwiftQueueJob {
                 return op.uuid == operation.uuid


import Foundation

internal class JobConstraint {

    func schedule(queue: SwiftQueue, operation: SwiftQueueJob) throws {

    }

    func run(operation: SwiftQueueJob) throws {

    }

}



    class DeadlineError: ConstraintError {}

    func schedule(queue: SwiftQueue, operation: SwiftQueueJob) throws {
        try check(operation: operation)
    }

    func run(operation: SwiftQueueJob) throws {
        try check(operation: operation)
    }

