菜鸟学习，请高手进来指点

- (NSMutableDictionary *) mutableDeepCopy {
NSMutableDictionary *returnDict = [[NSMutableDictionary alloc]
initWithCapacity:[self count]];

NSArray *keys = [self allKeys];

for (id key in keys) {
id oneValue = [self valueForKey:key];
id oneCopy = nil;

if ([oneValue respondsToSelector:@selector(mutableDeepCopy)])
oneCopy = [oneValue mutableDeepCopy];
else if ([oneValue respondsToSelector:@selector(mutableCopy)])
oneCopy = [oneValue mutableCopy];
if (oneCopy == nil)
oneCopy = [oneValue copy];
[returnDict setValue:oneCopy forKey:key];
[oneCopy release];
}
return returnDict;
}

[ if ([oneValue respondsToSelector:@selector(mutableDeepCopy)])
oneCopy = [oneValue mutableDeepCopy];
else if ([oneValue respondsToSelector:@selector(mutableCopy)])
oneCopy = [oneValue mutableCopy];
这一条语句判断的用处是什么？ 请高手指点
[解决办法]
判断oneValue是能响应mutableDeepCopy这个消息。就是说oneValue是不是有mutableDeepCopy方法！
[解决办法]
oneValue所属的类，应该有一个可选择的代理方法mutableDeepCopy，这句话，就是判断这个方法是否被实现了，如果被实现的话，就执行该方法