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.

Barry Wark · Accepted Answer · 2010-11-28 22:28:40Z

5

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.

answered Nov 28, 2010 at 22:28

Barry Wark

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3 Comments

Unis Over a year ago

Thanks for your clarification, so for best practice and to be safe i should always use the first method?.

Barry Wark Over a year ago

@Unis, if you are targeting modern runtime only, best practice would probably be to skip the instance variable; less code is better. If you need compatibility with older runtimes, you have no choice but to go with declaring the instance variable.

Kunday Over a year ago

Skipping the ivar declaration could be better because it makes the header file look less cluttered.

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