调用接受可选错误指针的方法
我正在尝试调用 MacRuby 中定义如下的方法：
NSPropertyListSerialization
---------------------------
+ (id)propertyListWithStream:(NSInputStream *)stream
options:(NSPropertyListReadOptions)opt
format:(NSPropertyListFormat *)format
error:(NSError **)error
最后一个参数必须是指针，所以我这样做：
err = Pointer.new '@'
data = NSPropertyListSerialization.propertyListWithStream plist,
options: KCFPropertyListMutableContainers,
format: KCFPropertyListBinaryFormat_v1_0,
error: err
但是，我收到此错误：
expected instance of Pointer, got `200' (Fixnum) (TypeError)
堆栈跟踪来自 error: err 行。
无论对象的类型如何，作为错误传递的错误都是相同的。它可以是 nil、指针、字符串或完全任意的类型，错误保持不变。
我不知道200 fixnum 来自哪里。当然不是我的代码（这个脚本中几乎没有比我粘贴的代码更多的代码）。
更新：在@whitequark和@alloy的帮助下解决了。这是为了在 iOS 模拟器中编辑 Safari 书签。您可以在此处查看如何读取/写入二进制plist文件
I'm trying to call a method in MacRuby that's defined like this:
NSPropertyListSerialization
---------------------------
+ (id)propertyListWithStream:(NSInputStream *)stream
options:(NSPropertyListReadOptions)opt
format:(NSPropertyListFormat *)format
error:(NSError **)error
The last argument has to be a pointer, so I'm doing this:
err = Pointer.new '@'
data = NSPropertyListSerialization.propertyListWithStream plist,
options: KCFPropertyListMutableContainers,
format: KCFPropertyListBinaryFormat_v1_0,
error: err
However, I get this error:
expected instance of Pointer, got `200' (Fixnum) (TypeError)
The stack trace comes from the error: err line.
This error is the same regardless of the type of the object passed as error. It can be nil, a Pointer, a string or a completely arbitrary type, the error stays the same.
I have no idea where 200 fixnum comes from. Certainly not my code (there is barely any more code in this script than what I pasted).
Update: Solved with the help of @whitequark and @alloy. This was for editing Safari bookmarks in iOS Simulator. You can see how to read/write binary plist files here
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多行语句的堆栈跟踪始终引用最后一行（即，如果错误不是由可定位子表达式引起的），并且fixnum 200是以
KCFPropertyList开头的常量之一。Stacktraces for multiline statements always refer to the last line (i.e. if the error is not caused by a locateable subexpression), and fixnum 200 is one of the constants beginning with
KCFPropertyList.根据 plist 的内容，您应该能够使用：
NSDictionary.dictionaryWithContentsOfFile(path)来读取它。Depending on the contents of the plist, you should be able to read it with:
NSDictionary.dictionaryWithContentsOfFile(path).