Gunter Winkler <guwi17@gmx.de> writes:
Hello,
I tried to use boost::zip_iterator to sort 2 parallel arrays. Unfortunatly gcc does not compile the appended example because it can not convert
boost::detail::iterator_category_with_traversal<std::input_iterator_tag, boost::random_access_traversal_tag>
to either std::bidirectional_iterator_tag or std::random_access_iterator_tag. Thus it cannot dispatch the correct stl::__copy_backward() procedure.
Is sort() not yet supported?
Here's the thing: std::bidirectional_iterator_tag and std::random_access_iterator_tag both would imply that the iterator statisfied the Forward Iterator Requirements. Forward Iterator Requirements say that *a must be T&. zip_iterator returns a tuple of references, not a reference itself, from its operator*. Therefore, you can't legally call it a Forward Iterator, and using either std::bidirectional_iterator_tag or std::random_access_iterator_tag would be lying. Now, _does_ sort actually need a Forward Iterator in order to do its work? It's not clear that it does, but the original iterator requirements didn't account for beasts like zip_iterator. It's a bad situation, and it's made worse because I don't know how to write a specification for sort() that would allow a zip_iterator to work. How would you describe the result? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com