You cannot join ranges of unrelated types. I can't imagine how this would work with unrelated types as in your example. What would you expect the resultant range from the join function to have for the value_type and reference type?

You should however be able to do this:

BOOST_FOREACH(const C c, join(a | transformed(to_C()), b | transforms(to_C()))

{

    // do something

}

 

Does this idiom work for your real world example?

Neil Groves