On 11 Feb 2011, at 23:50, Stefan Bidi wrote:
> On Fri, Feb 11, 2011 at 5:42 PM, David Chisnall <[email protected]> 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];
}
}
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