Porting @property

Porting properties in a fashion that works in ARC code and in mulle-objc is tricky. It is best if you can restrict yourself to assign, copy and retain.

Property deallocation

In Apple ARC, properties are automatically cleared during -dealloc. In Apple Manual Retain-Release Mode (MRR) you have to do it yourself during -dealloc.

In mulle-objc all properties that reference objects or pointers are cleared during -finalize by setting them to 0.

readonly properties - they have no setter - are not cleared. But in mulle-objc they are backed by an ivar. It is open to discussion if you want to release them in -dealloc for compatibility or use -finalize to break possible retain cycles.

Here is how to write -dealloc for compatiblity with MMR (also see ARC Porting tips):

#if __has_feature(objc_arc) || defined( __MULLE_OBJC__)
# define PROPERTY_RELEASE( p)
#else
# define PROPERTY_RELEASE( p)  [_p release]
#endif
#if __has_feature(objc_arc)
# define SUPER_DEALLOC()
#else
# define SUPER_DEALLOC( p)  [super dealloc]
#endif

- (void) dealloc
{
    PROPERTY_RELEASE( a)
    PROPERTY_RELEASE( b)
    PROPERTY_RELEASE( c)
    SUPER_DEALLOC()
}

Missing Attributes

atomic

Yup it’s gone. Use locking or the atomic operations provided by mulle-thread.

weak

Use assign instead.

strong

When declaring a property use copy or retain. You usually use copy for NSValue, NSDate, NSNumber and NSString arguments, and retain for everything else.

nullable

One of the strong points of Objective-C is its gracious handling of nil values, which simplifies coding a lot. Remember that messaging nil also produces nil. With the introduction of nonnull nullable was also introduced. It is superflous.

You can easily get rid of nullable compile errors with:

#define nullable

unsafe_unretained

Use assign instead.

class

Remove the property. Use static variables in your @implementation then write and declare + accessors for them.