其实和Java很类似的，浅拷贝要实现用NSCopying，深拷贝要实现NSMutableCopying，举个例子：

摘抄自：http://stackoverflow.com/questions/11329754/is-this-a-reasonable-pattern-for-implementing-nsmutablecopying

// BBMovie.h

@interface BBMovie : NSObject < NSCopying, NSMutableCopying >
@property(readonly, nonatomic, copy) NSString *title;
@end

@interface BBMutableMovie : BBMovie
@property(readwrite, nonatomic, copy) NSString *title;
@end

// BBMovie.m (note: compiling with ARC)

@interface BBMovie ()
@property(readwrite, nonatomic, copy) NSString *title;
@end

@implementation BBMovie
@synthesize title = _title;

- (id)copyWithZone:(NSZone *)zone
{
    BBMovie *copy = [[BBMovie allocWithZone:zone] init];
    if (copy) copy.title = self.title;
    return copy;
}

- (id)mutableCopyWithZone:(NSZone *)zone
{
    BBMutableMovie *copy = [[BBMutableMovie allocWithZone:zone] init];
    if (copy) copy.title = self.title;
    return copy;
}

@end

使用的时候：

[obj copy];
[obj mutableCopy];