template< class Delegate, class Arg, class Base>
class _closure_t
{
public:
   template<class Result>
   class TT:
      public Base
   {
    Result operator()(Arg x) const
    { 
        (_d.*_f)(x);
    }
   }
   template<>
   class TT<void>
   {
    void operator()(Arg x) const
    { 
       (_d.*_f)(x);
    }
   }
};