Abstract superclass initializers in Objective-C

gistfile1.m

#import <Foundation/Foundation.h>

@interface Parent : NSObject
@end

@implementation Parent
- (id)init;
{
  if (!(self = [super init]))
		return nil;
		
	if ([self class] == [Parent class]) {
		[NSException raise:@"Instantiate a subclass!" format:nil];
		return nil;
	}
	
	return self;
}

- (NSString *)description;
{
	return [NSString stringWithFormat:@"<%@:%p>", NSStringFromClass([self class]), self];
}
@end

@interface Child : Parent
@end

@implementation Child
- (id)init;
{
	if (!(self = [super init]))
		return nil;
		
	return self;
}
@end

int main(int argc, char *argv[]) {
	@autoreleasepool {
		Child *child = [[Child alloc] init];
		NSLog(@"%@", [child description]);
		
		Parent *parent = [[Parent alloc] init];
		NSLog(@"%@", [parent description]);
	}
}