Re: Selecting an overloaded (potentially templated) constructor.

Dear newsgroup.

This is my first post here, I hope I'm doing it right.

I wrote a circular iterator class which works as I intended but there
is a little quirk left which maybe you can help me to get rid of:

I want the constructor of my class to accept an iterator range and an
optional current iterator which defaults to the start iterator.
Additionally, it should accept an STL-style container (which will be
used from .begin() to .end()) and an optional current iterator which
defaults to the .begin()-iterator.

The problem is, when I use an array of non-const data to feed my class
(having a pointer to const data as a template argument), the compiler
(GCC) seems to pick the wrong constructor.

I reduced the problem to the following (hopefully minimal) example:

template <typename T>
struct my_class
{
 my_class(const T& begin, const T& end, const T& current = T()) :
   _begin(begin), _end(end), _current(current != T() ? current :
begin)
 {}
 template <typename Container> explicit
 my_class(Container& container, const T& current = T()) :
   _begin(container.begin()), _end(container.end()),
   _current(current != T() ? current : _begin)
 {}
 private:
 const T _begin;
 const T _end;
 T _current;
};

int main()
{
 float array[3] = { 1.5, 2.5, 3.5 };
 my_class<float*> first(array, array + 3);
 // this doesn't work:
 my_class<const float*> second(array, array + 3);
 // this, however, does:
 my_class<const float*> third(&array[0], array + 3);
 // even this works:
 my_class<const float*> fourth(array + 0, array + 3);
 // and with non-const data it also works:
 my_class<float*> fifth(array, array + 3);
}

The error message (in the line where "second" is initialized) is:
error: request for member 'begin' in 'container', which is of non-
class type 'float [3]'

The question is, I guess, how can I tell the compiler, that "array" is
not a container but just a pointer to the first array element.

I'm sure I could avoid this special case in my code, but somehow I got
curious ...

Thanks in advance for your help,
Matthias