Do synthesized instance variables work in iPhone SDK?

Question

I tried using Obj-C properties to synthesize not only the accessor methods, but also the instance variable. I ended up with an error saying something like "...must explicitly name an ivar...".
I was under the impression the iPhone ran the modern (64-bit) Objective-C runtime. I'm using xCode 3.x and iPhone SDK 2.2. Are synthesized instance variables not supported, or do I need to change some xCode/project configuration settings to activate this support (I'd really like to use it)?
Does the fact that I'm linking to the Sen Test Kit Framework, or running on a relatively old Intel MacBook Pro cause this problem? If the 2.2 SDK does not support synthesized instance variables, does iPhone SDK 3.0 beta support them?
Note that I would need the synthesized ivar support to work on the iPhone simulator too (obviously) so that I can do testing. Hopefully the iPhone simulator supports the modern Obj-C 2.0 runtime.
Thank You,
Eric

Answer 1

orangekay wrote:
A. I don't see that anywhere in the Objective-C 2.0 language specification, so I don't believe this has anything to do with the iPhone SDK.
B. I don't see any point in adding such a thing to the language as it accomplishes nothing that could not be handled with a standard ivar declaration.
This sounds like a feature you imagined.
Yeah, right I imagined it. Get a clue, will you?
http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/oc Properties.html#//apple_ref/doc/uid/TP30001163-CH17-SW3
In general the behavior of properties is identical on all runtimes (see Runtime Versions and Platforms in Objective-C 2.0 Runtime Programming Guide). There is one key difference: the modern runtime supports instance variable synthesis whereas the legacy runtime does not.
For @synthesize to work in the legacy runtime, you must either provide an instance variable with the same name and compatible type of the property or specify another existing instance variable in the @synthesize statement. With the modern runtime, if you do not provide an instance variable, the compiler adds one for you. For example, given the following class declaration and implementation:
@interface MyClass : NSObject {
float sameName;
float otherName;
@property float sameName;
@property float differentName;
@property float noDeclaredIvar;
@end
@implementation MyClass
@synthesize sameName;
@synthesize differentName=otherName;
@synthesize noDeclaredIvar;
@end
the compiler for the legacy runtime would generate an error at @synthesize noDeclaredIvar; whereas the compiler for the modern runtime would add an instance variable to represent noDeclaredIvar.