JSON與值類型的串行化

Question

我想使用基金會的JSONSerialization.data(withJSONObject obj: AnyObject, options opt: WritingOptions = []) throws -> Data。但是，我無法弄清楚如何將我的值類型轉換爲適合該方法使用的引用類型。

例如，試圖連載簡單字符串數組失敗，因爲該方法需要一個引用類型，而不是一個值類型：

root@1c6c66df21cf:/tmp# swift 
Welcome to Swift version 3.0 (swift-3.0-PREVIEW-3). Type :help for assistance. 
    1> import Foundation 
    2> JSONSerialization.data(withJSONObject: [String]()) 
error: repl.swift:2:48: error: argument type '[String]' does not conform to expected type 'AnyObject' 
JSONSerialization.data(withJSONObject: [String]()) 

鑄造不起作用：

root@1c6c66df21cf:/tmp# swift 
Welcome to Swift version 3.0 (swift-3.0-PREVIEW-3). Type :help for assistance. 
    1> import Foundation 
    2> let value = [String]() 
value: [String] = 0 values 
    3> let reference = value as! NSArray 
reference: Foundation.NSArray = <extracting data from value failed> 

Execution interrupted. Enter code to recover and continue. 
Enter LLDB commands to investigate (type :help for assistance.) 

我也嘗試以該版本的核心基金會unit tests爲例：

root@1c6c66df21cf:/tmp# swift 
Welcome to Swift version 3.0 (swift-3.0-PREVIEW-3). Type :help for assistance. 
    1> import Foundation 
    2> let value = [String]() 
value: [String] = 0 values 
    3> let reference = value.bridge() 
reference: Foundation.NSArray = <extracting data from value failed> 

error: Couldn't lookup symbols: 
    (extension in Foundation):Swift.Array.bridge() -> Foundation.NSArray 

參考系統信息：

root@1c6c66df21cf:/tmp# uname -a 
Linux 1c6c66df21cf 4.4.12-boot2docker #1 SMP Wed Jun 1 22:45:59 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux 
root@1c6c66df21cf:/tmp# swift --version 
Swift version 3.0 (swift-3.0-PREVIEW-3) 
Target: x86_64-unknown-linux-gnu 

Answer 1

使用.bridge()是正確的做法。該錯誤是特定於REPL的。編譯整個文件時不會發生這種情況：

root@1c6c66df21cf:/tmp# cat test.swift 
import Foundation 

let value = ["string"] 
let reference = value.bridge() 
let jsonData = try! JSONSerialization.data(withJSONObject: reference) 
print(String(data: jsonData, encoding: .utf8)!) 
root@1c6c66df21cf:/tmp# swift test.swift 
["string"] 
root@1c6c66df21cf:/tmp# swiftc -o test test.swift 
root@1c6c66df21cf:/tmp# ./test 
["string"]