Re: Leopard Properties and NSMutable Array

FROM : Jonathan Dann
DATE : Sun Jan 06 18:57:17 2008

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_______________________________________________
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