Re: some unsigned/NSInteger to NSUInteger changes in -gui

[Wolfgang Lux]

Sebastian Reitenbach wrote:

> 
> On Monday, April 9, 2012 22:37 CEST, Fred Kiefer <address@hidden> wrote: 
> 
>> I just checked the code in base and Eric seems to be right here. The 
>> type check code in NSUnarchiver (we aren't talking about keyed coding 
>> here) has a lot of HACK warnings, but it seems to do what we need here, 
>> allow for different integer types to be used interchangeable.
>> 
>> Please go ahead and apply this change.
> 
> Argh, now I recognized, I seem to broke at least Fisicalab and Addresses on 
> startup:
> 
> 2012-04-10 17:05:54.485 FisicaLab[10884] Exception occured while loading 
> model: expected unsigned int and got int
> 2012-04-10 17:05:54.508 FisicaLab[10884] Failed to load Gorm
> 2012-04-10 17:05:54.528 FisicaLab[10884] Cannot load the main model file 
> 'Fisica.gorm'
> 
> putting a breakpoint at NSException, I end up here:
> 
> Breakpoint 2, -[NSException raise] (self=0x205b8f608, _cmd=0x20d881a50) at 
> NSException.m:956
> 956       if (_reserved == 0)
> Current language:  auto; currently minimal
> (gdb) bt
> #0  -[NSException raise] (self=0x205b8f608, _cmd=0x20d881a50) at 
> NSException.m:956
> #1  0x000000020d409b65 in +[NSException raise:format:] (self=0x20d8816a0, 
> _cmd=Variable "_cmd" is not available.
> ) at NSException.m:835
> #2  0x000000020d4c88c2 in -[NSUnarchiver decodeValueOfObjCType:at:] 
> (self=0x206e20088, _cmd=0x20cf0dea0, type=0x20cd10b20 "I", 
> address=0x20dc2fd70) at NSUnarchiver.m:247
> #3  0x000000020cb2972b in -[NSTabView initWithCoder:] (self=Variable "self" 
> is not available.
> ) at NSTabView.m:634
> #4  0x000000020d4c8200 in -[NSUnarchiver decodeValueOfObjCType:at:] 
> (self=0x206e20088, _cmd=0x20d8dda40, type=0x20d728790 "@", 
> address=0x20dc2df70) at NSUnarchiver.m:662
> #5  0x000000020d4c627d in -[NSUnarchiver decodeArrayOfObjCType:count:at:] 
> (self=0x206e20088, _cmd=Variable "_cmd" is not available.
> ) at NSUnarchiver.m:574
> #6  0x000000020d3459de in -[GSMutableArray initWithCoder:] (self=0x20721e648, 
> _cmd=Variable "_cmd" is not available.
> ) at GSArray.m:553
> #7  0x000000020d4c8200 in -[NSUnarchiver decodeValueOfObjCType:at:] 
> (self=0x206e20088, _cmd=0x20cf42dd0, type=0x20cd157ca "@", 
> address=0x7f7fffff8798) at NSUnarchiver.m:662
> #8  0x000000020cb79dc3 in -[NSView initWithCoder:] (self=Variable "self" is 
> not available.
> ) at NSView.m:4740
> #9  0x000000020d4c8200 in -[NSUnarchiver decodeValueOfObjCType:at:] 
> (self=0x206e20088, _cmd=0x20d8dda40, type=0x20d728790 "@", 
> address=0x20dc2dc00) at NSUnarchiver.m:662
> #10 0x000000020d4c627d in -[NSUnarchiver decodeArrayOfObjCType:count:at:] 
> (self=0x206e20088, _cmd=Variable "_cmd" is not available.
> ) at NSUnarchiver.m:574
> ...
> (gdb) frame 3
> #3  0x000000020cb2972b in -[NSTabView initWithCoder:] (self=Variable "self" 
> is not available.
> ) at NSTabView.m:634
> 634           [aDecoder decodeValueOfObjCType: "I" at: &_selected_item];
> (gdb) list
> 629                 }
> 630             }
> 631           [aDecoder decodeValueOfObjCType: @encode(BOOL) at: 
> &_draws_background];
> 632           [aDecoder decodeValueOfObjCType: @encode(BOOL) at: 
> &_truncated_label];
> 633           _delegate = [aDecoder decodeObject];
> 634           [aDecoder decodeValueOfObjCType: "I" at: &_selected_item];
> 635           _selected = [_items objectAtIndex: _selected_item];
> 636         }
> 637       return self;
> 638     }
> 
> but in AppKit/NSTabView.h:  
> I have: NSUInteger _selected_item;
> 
> so I don't really understand, why the decoder thinks its getting an int?
> 
> Someone can help me understand how I broke that?

The problem is that existing archives are coded using int values rather than 
unsigned int values.
The only safe way to change the encoding from signed to unsigned values and 
vice versa is to increment the version number for objects. Furthermore you will 
need to check the version number while decoding and either decode a signed int 
(if you find an old object version) or an unsigned (if you find a new object 
version).
However, I don't think this is worth the hassles, so its better to revert your 
change (and if you are paranoid you could raise exceptions while encoding and 
decoding if the _selected_item attribute is out of range).

Wolfgang