當(dāng)方法當(dāng)作變量或者參數(shù)后就意味著我們可以在一個方法中定義新的方法，這給代碼結(jié)構(gòu)層次和訪問級別的控制帶來了新的選擇。

如下例的一個方法請求中調(diào)用了很多其他的函數(shù)，可是其他的函數(shù)在項目中可能就只有這個方法會調(diào)用到：

func appendQuery(var url: String,
                     key: String,
                   value: AnyObject) -> String {

    if let dictionary = value as? [String: AnyObject] {
        return appendQueryDictionary(url, key, dictionary)
    } else if let array = value as? [AnyObject] {
        return appendQueryArray(url, key, array)
    } else {
        return appendQuerySingle(url, key, value)
    }
}

func appendQueryDictionary(var url: String,
                               key: String,
                             value: [String: AnyObject]) -> String {
    //...
    return result
}

func appendQueryArray(var url: String,
                          key: String,
                        value: [AnyObject]) -> String {
    //...
    return result
}

func appendQuerySingle(var url: String,
                           key: String,
                         value: AnyObject) -> String {
    //...
    return result
}

可以考慮改成這樣的形式

func appendQuery(var url: String,
                     key: String,
                   value: AnyObject) -> String {

    func appendQueryDictionary(var url: String,
                                   key: String,
                                 value: [String: AnyObject]) -> String {
        //...
        return result
    }

    func appendQueryArray(var url: String,
                              key: String,
                            value: [AnyObject]) -> String {
        //...
        return result
    }

    func appendQuerySingle(var url: String,
                               key: String,
                             value: AnyObject) -> String {
        //...
        return result
    }

    if let dictionary = value as? [String: AnyObject] {
        return appendQueryDictionary(url, key, dictionary)
    } else if let array = value as? [AnyObject] {
        return appendQueryArray(url, key, array)
    } else {
        return appendQuerySingle(url, key, value)
    }
}