写一个 setter 方法用于完成 @property (nonatomic, retain) NSString *name，

写一个 setter 方法用于完成 @property (nonatomic, retain) NSString *name

写一个 setter 方法用于完成 @property (nonatomic, copy) NSString *name

答：

// retain

- (void)setName:(NSString *)str {

  [str retain];

  [_name release];

  _name = str;

}

// copy

- (void)setName:(NSString *)str {

  id t = [str copy];

  [_name release];

  _name = t;

}