General Iterator std::map Problem

[Bourgond Aries]

I'm having trouble getting some code to work; I do not know for sure why, but I think it has to do with the way my compiler (TDM-GCC) evaluates a map iterator.

Here is my wrapper code, which I will follow by my test code:

template <typename T, bool IS_CLASS>
class Citerator;

// If we are supplied an int, char,... , we must create an iterator around it.
template <typename TYPE>
class Citerator<TYPE, false> : public std::iterator<std::input_iterator_tag, TYPE>
{
public:

    Citerator(TYPE iterator):m_raw_iterator(iterator){}
    Citerator(const Citerator &iterator):m_raw_iterator(iterator.m_raw_iterator){}
    Citerator &operator=(const Citerator &iterator){m_raw_iterator = iterator.m_raw_iterator; return *this;}

    bool operator==(const Citerator &citerator){return m_raw_iterator == citerator.m_raw_iterator;}
    bool operator!=(const Citerator &citerator){return m_raw_iterator != citerator.m_raw_iterator;}

    TYPE &operator*(){return m_raw_iterator;}
    TYPE &operator->(){return m_raw_iterator;}

    Citerator &operator++(){++m_raw_iterator; return *this;}
    Citerator &operator++(int){m_raw_iterator++; return *this;}

    TYPE &get(){return m_raw_iterator;}

private:

    TYPE m_raw_iterator;

};

// If we are provided an iterator, we inherit from it.
template <typename TYPE>
class Citerator<TYPE, true> : public TYPE
{
public:
    using TYPE::TYPE;
    TYPE &get(){return *this;}
};

// The iterator that wraps around both integers and other iterators.
template <typename TYPE, bool IS_CLASS = std::is_class<TYPE>::value>
class Iterator : public Citerator<TYPE, IS_CLASS>
{
public:
    using Citerator<TYPE, IS_CLASS>::Citerator;
};

And my test code:

int main()
{
    Iterator<int> a(0), b(22);

    std::vector<int> ax;
    Iterator<std::vector<int>::iterator> c(ax.begin()), d(ax.end());

    std::map<std::size_t, std::vector<int>> bx;
    Iterator<std::map<std::size_t, std::vector<int>>::iterator> e(bx.begin()), f(bx.end()); // Error occurs here.
}

[LB]

What is the error message?

[Bourgond Aries]

@L B

error: no matching function for call to 'Iterator<std::_Rb_tree_iterator<std::pair<const long long unsigned int, std::vector<int> > > >::Iterator(std::map<long long unsigned int, std::vector<int> >::iterator)'|

[LB]

Clang gives better diagnostics:
http://coliru.stacked-crooked.com/a/025fc7ba1326ca4d

note: candidate constructor (inherited) not viable: no known conversion from 'iterator' (aka '_Rb_tree_iterator<value_type>') to '_Link_type' (aka '_Rb_tree_node<std::pair<const unsigned long, std::vector<int, std::allocator<int> > > > *') for 1st argument

Take a look at a simplified example:

http://coliru.stacked-crooked.com/a/57128b07c505bd43

It appears that when you try to inherit constructors you don't get the special ones (copy ctor, move ctor, etc).

[Bourgond Aries]

I find that rather odd, considering I have explicitly declared and defined a copy constructor in Citerator, which initializes a member.

[LB]

I see no such ctor between lines 34 and 38, nor 43 to 46.

[Bourgond Aries]

You are correct in that; I was thinking of the Citerator when the IS_CLASS is false.

Anyways; I added Citerator(TYPE t){*this = t;} to the Citerator IS_CLASS = true specialization; which does seem to work. I think I understand why this happened.

I'm also thinking about changing std::input_iterator_tag to std::random_access_iterator_tag ?

I read that here (http://en.cppreference.com/w/cpp/iterator/advance) that advance will exploit this for the benefit of the random access iterator's properties.

Thanks for the insight, I'm marking this as solved.

[Hippogriff]

Wow I never knew about inheriting constructors in C++11...I need to read more stuff. (I blame me still using VS2010 which doesn't support it).

Just popping in to say thanks for the new info!