自定义对象 实现 Copy 和 MutableCopy

如果是我们定义的对象，那么我们自己要实现NSCopying,NSMutableCopying这样就能调用copy和mutablecopy了。
举个例子：

@interface MyObj : NSObject
{
         NSMutableString *name;
         NSString *imutableStr;
         int age;
}
@property (nonatomic, retain) NSMutableString *name;
@property (nonatomic, retain) NSString *imutableStr;
@property (nonatomic) int age;
@end
@implementation MyObj
@synthesize name;
@synthesize age;
@synthesize imutableStr;
- (id)init
{
         if (self = [super init])
         {
                   self.name = [[NSMutableString alloc]init];
                   self.imutableStr = [[NSString alloc]init];
                   age = -1;
         }
         return self;
}
- (void)dealloc
{
         [name release];
         [imutableStr release];
         [super dealloc];
}
- (id)copyWithZone:(NSZone *)zone
{
         MyObj *copy = [[[self class] allocWithZone:zone] init];
         copy.name = [name copy];
         copy.imutableStr = [imutableStr copy];
//       copy->name = [name copyWithZone:zone];;
//       copy->imutableStr = [name copyWithZone:zone];//
         copy->age = age;
         return copy;
}
- (id)mutableCopyWithZone:(NSZone *)zone
{
         MutableCopyObject  *mutableCopy = [[[self class] alloc] init];
         copy.name = [self.name mutableCopy];
         copy.age = [imutableStr mutableCopy];
         return copy;
}