[Bug libstdc++/59042] Declaration of back_insert_iterator::value_type is incorrect

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59042

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Your code is not valid, you should be using typename
iterator_traits<OutputIterator>::value_type