问Swift 3:如何从[String: AnyObject]转换为[String: String]？

EN

// (example) source dict
let dict: [String: AnyObject] = ["foo": "1" as AnyObject,
                                 "bar": 2 as AnyObject,
                                 "baz": "3" as AnyObject]

// target dict
var targetDict = [String: String]()
for (key, value) in dict {
    if let value = value as? String { targetDict[key] = value }
} // targetDict: ["foo": "1", "baz": "3"]

if let castedDict = dictionary as? [String: String] {
    print("Converted successfully: \(castedDict)")

} else {
    print("Failed to cast the dictionary")
}