On Sep 5, 2009, at 21:15, Adam R. Maxwell wrote:
>
> On Sep 5, 2009, at 11:27 AM, Christiaan Hofman wrote:
>
>>
>> On Sep 5, 2009, at 19:59, Adam R. Maxwell wrote:
>>
>>>
>>> On Sep 5, 2009, at 10:43 AM, Christiaan Hofman wrote:
>>>
>>>> And now I know why PDFKit doesn't work on 64 bits. They are really
>>>> messing up writing to ivars. Remember they use weird private
>>>> classes
>>>> to hide the ivars. This means they must be using runtime
>>>> functions to
>>>> read/write to these ivars, because these private classes don't have
>>>> accessors.
>>>
>>> Is it really using runtime functions? I've done this by
>>>
>>> @class PublicClassIvars;
>>>
>>> @interface PublicClass : NSObject
>>> {
>>> @private
>>> PublicClassIvars *_ivars;
>>> }
>>> @end
>>>
>>> /// In the implementation of PublicClass, declare the ivars
>>>
>>> @interface PublicClassIvars : NSObject
>>> {
>>> @public
>>> id _representedObject;
>>> NSInteger _type;
>>> }
>>> @end
>>>
>>> and you can access it in PublicClass by
>>>
>>> NSInteger t = _ivars->_type;
>>> id obj = _ivars->_representedObject;
>>>
>>> Basically this is the Pimpl idiom, using an object instead of an
>>> opaque pointer, and it's pretty easy unless you have object types
>>> and need to manage memory. It would be interesting to set a
>>> breakpoint on the objc runtime functions and see if PDF Kit is
>>> calling them. If so, that's really the hard way of doing it; you
>>> might as well use indexed ivars!
>>>
>>
>> That sounds very dangerous, especially in view of Objective-C 2.0 and
>> 64 bits. Moreover, the compiler complains very hard, and the docs say
>> not to use @defs in 64-bits. Remember they're making objects more and
>> more opaque. Anyway, PDFKit for sure does it the hard way by adding
>> all those private ivar wrapping objects.
>
> No, this works fine in 64 bit (I use it in FileView); the important
> part is @public in the declaration of PublicClassIvars, which
> obviates the need for @defs since you already have access to _ivars
> from PublicClass. For true opaque objects, you'd use @dynamic, but
> then I think you have to use @property accessors...which would
> eliminate the private ivar object also.
>
But PDFKit does not use @public, and the docs say not to use @defs.
Christiaan
>
> #import <Foundation/Foundation.h>
>
> @class PublicClassIvars;
>
> @interface PublicClass : NSObject
> {
> @private
> PublicClassIvars *_ivars;
> }
> @end
>
> @interface PublicClassIvars : NSObject
> {
> @public
> id _representedObject;
> NSInteger _type;
> }
> @end
>
> @implementation PublicClassIvars
> @end
>
> @implementation PublicClass
>
> - (id)init
> {
> self = [super init];
> if (self) {
> _ivars = [PublicClassIvars new];
> _ivars->_representedObject = [NSObject new];
> _ivars->_type = 1;
> }
> return self;
> }
>
> - (NSString *)description
> {
> return [NSString stringWithFormat:@"%@:\n\trepresented object = %@
> \n\ttype = %d", [super description], _ivars->_representedObject,
> _ivars->_type];
> }
>
> @end
>
> int main (int argc, char const *argv[])
> {
> NSAutoreleasePool *pool = [NSAutoreleasePool new];
>
> PublicClass *x = [PublicClass new];
> NSLog(@"%@", [x description]);
>
>
> return 0;
> }
>
>
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