simpleStub.swift

// helper global function
func stub<T>(of v: T) -> T {    
  return nil!
}
protocol Database {
  func addUser(name: String) -> Bool
}
class DatabaseStub: Database {    
  lazy var addUserAction = stub(of: addUser) // (String) -> Bool
  func addUser(name: String) -> Bool {     
    return addUserAction(name)    
  }
}