在迭代器上使用复制构造函数

Question

I'm trying to make iterator. As a constructor I have:

iterator(Node* node)
{
    it = node;
}

and copy constructor:

iterator(const iterator& x)
{
    it = x.it;
}

I was told that using first one is not a good idea while having second one(which is better)

I'm not sure how to use second approach in methods like this:

typedef iterator<Key, Info> ringIterator;

ringIterator begin()
{
    return ringIterator(any);
}

Answer 1

A copy constructor is a constructor, that accepts a (usually, but not necessarily, constant) reference to the same type.

Therefore, iterator(Node *) is not a copy constructor. It is a constructor from some internal entity of your collection.

You do need that constructor in the implementation of the begin() (and end() and other methods returning iterators) of the collection. However:

1. It should be marked explicit so it won't be used for implicit conversion.
2. It should preferably not be visible outside the two classes. Probably by making it private and using suitable friend declaration. You should probably nest the iterator and the internal Node type in the collection; that way the Node itself can be private (but you don't show the complete structure of the collection you are writing, so I can't say for sure how to put this together).