Am 12.08.2008 um 19:05 schrieb Jason Coco:
On Aug 12, 2008, at 12:50 , Klaus Backert wrote:
About $Null:
It it were a reserved word, it would be documented so.
The "Archives and Serializations Programming Guide for Cocoa" says:
Keyed Archives
...
Naming Values
...
You should avoid using “$” as a prefix for your keys. The keyed
archiver and unarchiver use keys prefixed with “$” for internal
values. Although they test for and mangle user-defined keys that
have a “$” prefix, this overhead slows down archiving performance.
...
In this case, however, it's the actual value being encoded... not
the key name. Also, if you read it, it suggests that you shouldn't
use it for performance reasons. It specifically states that it is
supposed to properly mangle the $ in a key name (causing the
performance loss)...
That's right. Sorry, I confused this. But talking about ... I read
nothing in the documentation what using $-prefixed *keys* for
internal values *exactly* does. It improves performance, okay, but it
can be anything else, and a different thing tomorrow. I handle this
"implementation detail" in the usual way. I will stay away from $-
prefixed keys.
Back to $-prefixed *values*:
Gerriet Denkmann already realized something – which is not
documented, as far as I know. A keyed archive contains a $object
array, and the element $object[0] has the value $null. Implementation
detail!
I performed a test with my current project. I changed a certain value
of a string variable to $null, saved it as a keyed archive in binary
property list format – with the $null value anywhere in the "middle"
–, opened the saved archive in a new document, and ...
***crash***:
2008-08-12 20:04:58.549 Blotto[24783] NSExceptionHandler has recorded
the following exception:
NSInvalidArgumentException -- *** -[NSPlaceholderDictionary
initWithObjects:forKeys:]: number of objects (0) not equal to number
of keys (21)
Stack trace: 0x966eaf10 0x92c10e0c 0x92c552a0 0x92c18fc8
0x92bfaea4 0x92bfa688 0x00007bd8 0x92bfaea4 0x92bfa688
0x0001840c 0x000160e8 0x93ac6344 0x00012acc 0x939504a8
0x00012e20 0x93ac5634 0x9394f960 0x93acc1fc 0x93acc03c
0x93acbec0 0x938358b4 0x93890094 0x9388fe18 0x9388f8c0
0x9388f50c 0x93799058 0x93790960 0x93881458 0x00004334
0x00003258 0x00002f5c 0x00001000
2008-08-12 20:04:58.550 Blotto[24783] NSExceptionHandler will now
suspend the current thread and wait for debugger attachment
_NSExceptionHandlerExceptionRaiser (in ExceptionHandling)
+[NSException raise:format:] (in Foundation)
-[NSDictionary initWithObjects:forKeys:] (in Foundation)
-[NSDictionary initWithCoder:] (in Foundation)
__decodeObjectBinary (in Foundation)
__decodeObject (in Foundation)
-[BloWorld initWithCoder:] (in Blotto)
__decodeObjectBinary (in Foundation)
__decodeObject (in Foundation)
-[BloDocument readPListFromData:error:] (in Blotto)
-[BloDocument readFromData:ofType:error:] (in Blotto)
-[NSDocument readFromFileWrapper:ofType:error:] (in AppKit)
-[YetDocument readFromFileWrapper:ofType:error:] (in Blotto)
(YetDocument.m:153)
-[NSDocument readFromURL:ofType:error:] (in AppKit)
-[YetDocument readFromURL:ofType:error:] (in Blotto) (YetDocument.m:172)
-[NSDocument _initWithContentsOfURL:ofType:error:] (in AppKit)
-[NSDocument initWithContentsOfURL:ofType:error:] (in AppKit)
-[NSDocumentController makeDocumentWithContentsOfURL:ofType:error:]
(in AppKit)
-[NSDocumentController openDocumentWithContentsOfURL:display:error:]
(in AppKit)
-[NSDocumentController openDocument:] (in AppKit)
-[NSApplication sendAction:to:from:] (in AppKit)
-[NSMenu performActionForItemAtIndex:] (in AppKit)
-[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] (in
AppKit)
-[NSMenu performKeyEquivalent:] (in AppKit)
-[NSApplication _handleKeyEquivalent:] (in AppKit)
-[NSApplication sendEvent:] (in AppKit)
-[NSApplication run] (in AppKit)
_NSApplicationMain (in AppKit)
_main (in Blotto) (main.m:10)
__start (in Blotto)
start (in Blotto)
0x00001000 (in Blotto)
q.e.d.
Greetings
Klaus
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