Synthesizing a property without instance variables

Question

I thought I understood @property and @synthesize, but I did some experimenting and I can't figure out why the below (what I thought was broken) code works.

As you can see, there's no instance variable that corresponds to the name property. Does Objective-C somehow create an instance variable if it doesn't find an instance variable with the same name and type?

Header:

#import <Foundation/Foundation.h>  @interface AddressCard : NSObject {  }  @property (copy, nonatomic) NSString *name; -(void) print;  @end 

Implementation:

#import "AddressCard.h"  @implementation AddressCard  @synthesize name;  -(void) print {     NSLog(@"Name=%@", self.name); }  -(void) dealloc {     [name release];     [super dealloc]; }  @end 

Test:

int main (int argc, const char * argv[]) {     NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];      AddressCard *ac = [[AddressCard alloc] init];     ac.name = @"Brandon";     [ac print];      [ac release];      [pool drain];     return 0; } 

Answer 1

The quick answer is: "yes". In Objective-C 2.0, synthesized properties will automatically create the corresponding ivars as required.

Apple's documentation has some more details.

Important: As pointed out by Tommy (note: this is from the legacy docs - please see the latest information):

In Objective-C 2.0 on either of the modern runtimes (ie, Intel 64bit and ARM) properties can be added to classes 'dynamically' (that is, at runtime but only before the creation of any instances — not particularly dynamic compared to the rest of the runtime). However, this can't be done on either of the two older runtimes (ie, Intel 32bit and PowerPC). It's therefore not really something you want to use on shipping software for the Mac or during development for iOS (since the simulator is a 32bit Intel application and can't create instance variables at runtime)

Answer 2

You can omit instance variable declaration only for 64-bit architecture