> On 11 Feb 2011, at 23:50, Stefan Bidi wrote:
>
>> On Fri, Feb 11, 2011 at 5:42 PM, David Chisnall <
address@hidden> wrote:
>> Hi Stefan,
>>
>> I've not looked at the code in detail, but I thought you were creating a private subclass for the old and new behaviours - would it not be possible to simply return a private subclass instance from the constructors and not change the ivar layout of the superclass?
>>
>> I really haven't got a clue how to go about getting something like that done. I'm still at the "getting my feet wet" stage of OOP + ObjC. I'll have a look at how NSString and it's subclasses are implemented, but I'll probably need someone holding my hand, at least part of the way.
>
> The idea of using a subclass sounds good, and it's quite easy.
> I wouldn't recommend looking at NSString as an example though ... that's a much, much more complex case than would be needed.
>
> The simple subclassing solution would be to keep the old implementation in the base class, and just modify the +allocWithZone: method.
> eg.
>
> + (id) allocWithZone: (NSZone*z)
> {
> if (using_new_api && [NSDateFormatter class] == self)
> {
> // If the subclass calls the super implementation, the check for the class will prevent recursion.
> return [subclass allocWithZone: z];
> }
> else
> {
> return [super allocWithZone: z];
> }
> }