I'm new to the newsletter, so I might not be in line with standard netiquette here... In case please make me aware of my shortcomings, thanks :-)

I noticed that it is not possible to retrieve the output stream used by a std::ostream_iterator,
even if it would be useful in a few contexts like the following example:

std::string print_vector( const std::vector<int> & v )
    std::stringstream s;
    copy( begin(v), end(v), std::ostream_iterator<int>( s, ", " ) );
    return s.str();

If there was a method ostream_iterator<...>::stream() that returns the reference to the stream captured by the iterator,
it would be possible to make the above code more concise:

template<typename T>
std::string print_vector( const vector<T> & v )
    return copy( begin(v), end(v), ostream_iterator<int>( stringstream{}, ", " ) ).stream().str();

Naturally the extension should apply to all input/output iterator facades in the STL