Effective Objective-C 2.0 编写高质量iOS与OS X代码 对象等同性

- (BOOL)isEqual:(id)object
{
     if(self == object) return YES;
     if([self class] != [object class] ) return NO;
     ConcreteId *otherId = (ConcreteId*)object;
     if(![someProperty isEqual:otherId.someProperty])
          return NO;
     // ……… 比较其他属性值
     return YES;
}

- (BOOL)isEqual:(id)object
{
     if([self class] ==[ object class ])
     {     
          return [self isEqualToPerson:(EOCPerson*)object};
     }else {
          return [self isEqual:object];
     }
}

NSMutableSet *set = [NSMutableSet new];
NSMutableArray *arrayA = [@[@1, @2] mutableCopy];
[set addObject:arrayA];
NSLog(@“set = %@“,set);
// set = {((1,2))}

NSMutableArray *arrayB = [@[@1, @2] mutableCopy];
[set addObject:arrayB];
NSLog(@“set = %@“,set);
// set = {((1,2))} 

NSMutableArray *arrayC = [@[@1] mutableCopy];
[set addObject:arrayC];
NSLog(@“set = %@“,set);
// set = {((1),(1,2))}  

[arrayC addObject:@2];
NSLog(@“set = %@“,set);
// set = {((1,2),(1,2))}  

NSSet *setB = [set copy];
NSLog(@“setB = %@“,setB);
// setB = {((1,2))}