问Swift闭包:不能用参数列表调用函数

EN

import Alamofire

typealias ProgressBlock = (Double) -> Void
typealias CompletionBlock = (Bool, ErrorType?) -> Void

class ExampleDataSource {
    func fetchData(progress: ProgressBlock?, completion: CompletionBlock?) {
        // Here we use the Alamofire Dependency for progress reporting simplicity.
        Alamofire.request(.GET, "https://www.myexampledomain.com")
            .progress { bytesRead, totalBytesRead, totalBytesExpectedToRead in
                // bytesRead, totalBytesRead, and totalBytesExpectedToRead are Int64
                // so we must perform unit conversion
                let progressPercentage = Double(totalBytesRead) / Double(totalBytesExpectedToRead)
                // here we optionally call the ProgressBlock 'progress' and pass it the progressPercentage
                progress?(progressPercentage)
            }
            .response { request, response, data, error in
                // here we usually parse the data, but for simplicity we'll
                // simply check to see if it exists.
                let completionFlag = (data != nil)
                // note that NSError? is interchangable with ErrorType?
                completion?(completionFlag, error)
        }
    }
    func performTasks() {
        // first we'll set up our closures...
        let progressBlock: ProgressBlock = { progress in
            // here we update the UI or whatever 
            // the nice thing about the Alamofire dependency is
            // that it's thread-safe :]
        }
        let completionBlock: CompletionBlock = { success, error in
            // here we do whatever we need to do when the
            // network operation finishes, or handle the 
            // errors appropriately
        }
        // then we'll pass them into our fetchData method
        fetchData(progressBlock, completion: completionBlock)
    }
}