Do declared properties require a corresponding instance variable?

objective-c instance-variables declared-property
indragie picture indragie · Jun 19, 2010 · Viewed 28.7k times · Source

Do properties in Objective-C 2.0 require a corresponding instance variable to be declared? For example, I'm used to doing something like this:

MyObject.h

@interface MyObject : NSObject {
NSString *name;
}
@property (nonatomic, retain) NSString *name;
@end

MyObject.m

@implementation
@synthesize name;
@end

However, what if I did this instead:

MyObject.h

@interface MyObject : NSObject {
}
@property (nonatomic, retain) NSString *name;
@end

Is this still valid? And is it in any way different to my previous example?

Answer

jbrennan picture jbrennan · Jun 19, 2010

If you are using the Modern Objective-C Runtime (that's either iOS 3.x or greater, or 64-bit Snow Leopard or greater) then you do not need to define ivars for your properties in cases like this.

When you @synthesize the property, the ivar will in effect be synthesized also for you. This gets around the "fragile-ivar" scenario. You can read more about it on Cocoa with Love

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