Obj-C Accessors and ARC

Question

I wrote a very basic class to play with the new ARC and accessor methods, just to get a feel for how they work. From what I've read, the ARC should replace manual reference counting, right? But I get a problem with my accessor methods.

Here's my Interface/Implementation for my Container class:

// interface
@interface Container : NSObject {
   NSMutableString *string;
}

- (NSMutableString *)string;
- (void)setString:(NSMutableString *)aString;

@end

// implementation
@implementation Container

- (NSMutableString *)string
{
   return string;
}

- (void)setString:(NSMutableString *)aString
{
   string = aString;
}

- (NSString *)description
{
   return [NSString stringWithFormat:@"inner string = %@", string];
}

@end

It seems alright to me, all the reference counting details are handled by the ARC I believe. The problem occurs in the main method:

Container *myContainer = [[Container alloc] init];
  NSMutableString *aString = [NSMutableString stringWithString:@"Hello!"];

[myContainer setString:aString];

NSLog(@"%@", myContainer);

[aString setString:@"Bye!"];

NSLog(@"%@", myContainer);

aString = [myContainer string];
[aString setString:@"Bye, again!"];

NSLog(@"%@", myContainer);

It seems that aString points to the string member variable, which means when I change aString I also change string with it. I tried releasing aString from the main() method but then I get a compiler error. How do I fix this? Do I use the copy method, or is there another way?

Answer 1

rcplusplus,

You asked:

It seems that aString points to the string member variable, which means when I change aString I also change string with it. I tried releasing aString from the main() method but then I get a compiler error. How do I fix this? Do I use the copy method, or is there another way?

The way to release any ARC item is to set it to nil . This tells the compiler you are through with this item. It is released in the assignment.

Example:

[myContainer setString: nil];
myContainer.string = nil;

or, from within your class:

string = nil;

Andrew