dynamic - Objective C: Why do we declare ivars in the .h member area if @property seems to do it automatically?

Question

In implementing an interface it seems the common method in tutorials and literature is to declare an ivar and then set the @property then @synthesize.

@interface MyClass : NSObject {
NSString *myString;
}

@property (nonatomic, retain) NSString *myString;
@end

However, omitting the explicit declaration and just putting @property has the same effect.

@interface MyClass: NSObject {
}

@property (nonatomic, retain) NSString *myString;
@end

So how come most people use @property and an explicit declaration? Is it bad form not to?

Answer 1

It used to be necessary. There are two different versions of the Objective-C runtime: a 32-bit-only "legacy" runtime (the old one) and a 32/64-bit runtime (the new 32-bit runtime is only used on iOS devices and for the iOS simulator).

I think the only place this is still necessary is when you're running the app in 32-bit mode (either 10.5 or 10.6). Everywhere else (64-bit Leopard, 64-bit Snow Leopard, Lion, iOS) uses the newer runtime that has "automatic ivar synthesis", and the resulting ivars are referred to as "synthesized ivars".