Leopard Properties and NSMutable Array

[Jonathan Dann]

On 6 Jan 2008, at 03:43, Bill Bumgarner wrote:

> On Jan 5, 2008, at 7:10 PM, André Pang wrote:
>> On 06/01/2008, at 12:53 PM, Bill Bumgarner wrote:
>>> Which, unfortunately, is the alternative.   There is an  
>>> enhancement request already to offer a mutablecopy keyword.
>> Is there actually a use for a 'mutablecopy' keyword?  I ran into  
>> the same problem as Jonathan, but then realised that retain  
>> semantics are typically what you want for a mutable object.  I  
>> can't quite think of a case where a mutable copy of the array in  
>> the class would actually be useful.
>>
>> (Maybe that thought can be used as a possible warning: if you  
>> define a property for a type that obeys the NSMutableCopying  
>> protocol, perhaps a warning can be emitted if you use copy rather  
>> than retain...)
>
> There are uses for mutablecopy in that there has been more than one  
> person that has filed a request for it. :)
>
> Seriously, though, there are cases where mutablecopy makes a lot of  
> sense.  Specifically, if your object model is such that your object  
> wants to take ownership of the contents of the array and changes  
> therein.   It is much easier to guarantee that a mutable array's  
> contents haven't changed if you have isolated ownership of said  
> mutable array;  copying on set and returning a copy on get.
>
> Of course, that has efficiency / performance / memory implications  
> and, thus, balance must be maintained between performance and bullet  
> proof.
>
> b.bum
>

What I really wanted was the ability to declare the mutable array as a  
property as a I've really grown to like the 'dot syntax'.  So here is  
the solution that seems to have worked:

@interface Foo : NSObject {
	NSMutableArray *array;
}

@property(copy) NSMutableArray *array;

- (void)setArray:(NSMutableArray *)a;
- (NSMutableArray *)array;

@end

@implementation

@dynamic array;

- (void)setArray:(NSMutableArray *)a;
{
	if (array != a) {
		[array release];
		array = [a mutableCopy];
	}
}

- (NSMutableArray *)array;
{
	[return array];
}

@end

In my main.m I can then call [array addObject:[NSString string]];  
without an error or compiler warnings.

I think I could pass the setter an NSArray too as NSArray conforms to  
NSMutableCopying.  Is there anything that I missed, could this go  
horribly wrong somewhere?

Jon