Writing an iterator that makes several containers look as one

Question

Consider the following simplified example and desired output:

class A
{
    class combined_iterator
    {
        ????
    }
    typedef ??? t_combined_it;

         


        

Answer 1

boost::join is what you're looking for. You can also study the implementation, especially how to derive the lowest common denominator for container traversal, reference and return value types. To quote:

The intention of the join function is to join two ranges into one longer range.

The resultant range will have the lowest common traversal of the two ranges supplied as parameters.

Note that the joined range incurs a performance cost due to the need to check if the end of a range > has been reached internally during traversal.