swift如何使用后卫同时展开可选和铸造类型

我有以下代码.该response.result.value类型是Optional(AnyObject),我要检查

它的类型 [[String: AnyObject]]

打开可选项

检查数组的计数

如果...返回...声明,我更喜欢一个线卫

Alamofire.request(.GET, API.listArticle).responseJSON {
    response in

    print(response.result.value)

    guard let articles = response.result.value as? [[String: AnyObject]] where articles.count > 0 else {
        return
    }

    for article in articles {
        let entity = NSEntityDescription.insertNewObjectForEntityForName("Article", inManagedObjectContext: DBHelper.context()) as! Article
        entity.title = article["title"]
        entity.content = article["content"]

    }
}

错误是article["content"]行,

cannot subscript a value of type Dictionary with an index of type String.

我还需要检查是否title存在article？它会崩溃还是什么都不做？