objective c - What is the different between Instance variable vs property ?

Question

I've seen a lot of codes that do this:

@interface Test0 : NSObject {
        @private int iVar;
}
@property (readwrite,assign) int iVar;
@end

and some other codes:

@interface Test0 : NSObject {
}
@property (readwrite,assign) int iVar;
@end

I know that you use the @synthesize iVar to tell the compiler to generate the getter and the setter methods for the property iVar.

My questions: do we need to declare the @private int iVar; instance variable? What the advantage of doing so? What is the best practice of declaring instance variables vs property? does the compiler link the instance variable with the property?

Thanks in advance.

Answer 1

Modern Objective-C runtimes and compilers that use non-fragile base classes (IIRC, the 64-bit runtime on OS X and the iOS 4.0 and higher runtimes) allow you to omit the instance variable. Your first example is required for older runtimes, the later is all that is required in modern runtimes.