Forcing a subclass to provide an initialization method

class Edge(EdgeBase):
    def __new__(cls, left, right):
        self = super(Edge, cls).__new__(cls, left, right)
        self._hash = hash(self.left) * hash(self.right)
        return self

    def __hash__(self):
        return self._hash

Mammal *mammal = [[Dog alloc] init]; //Dog is a subclass of Mammal

if ([mammal isKindOfClass:[Dog class]]) {
    [(Dog *)mammal bark];
}

@interface Vehicle : NSObject
  -(void)logDetails __attribute__((objc_requires_super));
@end

@implementation Car
  -(void) logDetails {
} // WARNING: Method possibly missing a [super logDetails] call

@protocol VehicleLogger <NSObject>

-(void)logDetails;

@end

@implementation Car <VehicleLogger>

-(void)logDetails {
   [super logDetails];
   //Do more stuff here, if I want
}