BNRItemStore is a singleton, and I was confused on why super allocWithZone: must be called instead of plain old super alloc. And then override alloc instead of allocWithZone.
#import "BNRItemStore.h"
@implementation BNRItemStore
+(BNRItemStore *)sharedStore {
static BNRItemStore *sharedStore = nil;
if (!sharedStore)
sharedStore = [[super allocWithZone: nil] init];
return sharedStore;
}
+(id)allocWithZone:(NSZone *)zone {
return [self sharedStore];
}
@end
[super alloc] will call through to allocWithZone:, which you've overridden to do something else. In order to actually get the superclass's implementation of allocWithZone: (which is what you want there) rather than the overridden version, you must send allocWithZone: explicitly.
The super keyword represents the same object as self; it just tells the method dispatch mechanism to start looking for the corresponding method in the superclass rather than the current class.
Thus, [super alloc] would go up to the superclass, and get the implementation there, which looks something like:
+ (id) alloc
{
return [self allocWithZone:NULL];
}
Here, self still represents your custom class, and thus, your overridden allocWithZone: is run, which will send your program into an infinite loop.
From Apple's documentation:
This method exists for historical reasons; memory zones are no longer used by Objective-C.
