lvalue-ness resurrection in transform_iterator

[Shunsuke Sogame <pstade.mb@…>]

The patch for a function returning lvalue. See: ​http://lists.boost.org/Archives/boost/2007/12/131439.php

[Shunsuke Sogame <pstade.mb@…>]

extracts pure traversal tag

[Dave Abrahams]

If I understand correctly what your patch is doing, you are effectively determining whether the resulting transform_iterator<...> satisfies the access requirements of ForwardIterator (and thus, RandomAccessIterator) by looking at the lvalueness of the transformed result_type. Unfortunately, that's not a valid way to make the determination, because the resulting iterator doesn't suddenly become multipass just because of a change in the reference type. In fact, most of the standard's InputIterators return references from their operator*.