Interval streaming does not work for std::wstring

[gast128@…]

Stream operators for intervals only work for std::string, e.g. the following code gives a compilation error:

void Test()
{
   typedef boost::icl::interval_set<int> IntervalSet;

   IntervalSet setSimple;
   setSimple.add(1).add(3);

   for (const IntervalSet::value_type& r : setSimple)
   {
      std::wstringstream wsstr;
      wsstr << r;
   }
}