For istream_iterator or ostream_iterator, the operator '<<' and '>>' are used to serialize the data. Have anyone ever needed another operator (typically for serializing to another format, for example binary) ? To implement this, it seems possible to add the serializing operator to istream_iterator, as an extra template argument, which would by default use the existing operator>>. In other words : template, typename _Dist = ptrdiff_t> class istream_iterator { ... ... would be replaced by something like : template, typename _Dist = ptrdiff_t, typename _SerializingOperator = XXXXX > class istream_iterator { ... XXXXX would represent the existing operator>> for this data type. On the other hand, 'operator>>' is not a method of class _Tp, but a friend method. So, how to specify it are a default template argument ?