Synthesize by Default

So, in my previous post, I told you I was excited about the "synthesize by default" functionality that's now available in LLVM 1.5. And I am, very much so. But it turns out there's a caveat that tempers my excitement at the moment.

With synthesized iVars, we've had direct access to the underlying synthesized variable for a while now, so if you created a class like this:

#import <UIKit/UIKit.h>

@interface MyViewController : UIViewController 
{
}
@property (nonatomic, retain) NSString *foo;
@end

You're able to access the NSString variable foo that backs the property of the same name within the scope of your class. So, in your dealloc method, you can do this, to give one common example:

- (void)dealloc
{
    [foo release], foo = nil;
    [super dealloc];
}

However, if you enable the "synthesize by default" feature in LLVM 1.5 and use it, meaning you don't actually have a @synthesize statement for the foo property, you lose this direct access to the underlying variables, leaving you with a bit of a conundrum - how do you do your memory cleanup without unintentionally triggering unwanted functionality, such as those in a lazy accessor or some more involved mutators.

Earlier today, I tweeted a question asking about the correct way to deal with this situation. After a bit of a Who's on First-like back and forth with many smart people, it finally came out that this is a bug in LLVM, not an intentional design decision. Hopefully it will be fixed before too long, but in the meantime, the best answer is probably to just keep using @synthesize.

Thanks to a whole bunch of people on Twitter, many of whom I'm sure I missed!

Modern ABI & No More @Synthesize

I haven't talked about one of my favorite new features of Xcode 4 and LLVM, because I wasn't sure of the NDA status. However, the cat's out of the bag now, so I feel like it's safe to mention. The iPhone Simulator in Xcode 4 now uses the Modern ABI (yet it's still correctly uses 32-bit datatypes!), so we can use synthesized instance variables in our iPhone applications and use the simulator. On top of that, if you choose to use LLVM instead of GCC, one of the (many) benefits you'll get is that @synthesize declaration is now assumed. If you don't need to specify anything on the @synthesize declaration (like a different setter or getter name) and your property isn't @dynamic, you can justleave it off. This feature isn't turned on by default (yet), but see Pilky's blog post for instructions on enabling this feature.

Less code to write? Boo-yeah! Count me in!

I believe (though I haven't confirmed this yet) that you can write code this way and still target older releases back to 3.0. If anyone knows otherwise, please let me know and I'll spread the word, though.