[boost] [optional] optional<T &> and the arrow operator

9 Feb 2007

      I’ve discovered that you can’t use the arrow operator with an object 
of type optional<T &>;  For instance , the following code fails:

   vector<double> v;
   optional<vector<double> &> pv(v);
    pv->push_back(2);

The code

   (*pv).push_back(2)

succeeds.

On MSVC 7.1 on Windows XP I get the following error message: (I get a 
similar one using gcc 3.4 on Unix).

c:\code\boost\optional\optional.hpp(371) : error C2664: 
'boost::optional_detail::optional_base<T>::pointer_const_type 
boost::optional_detail::optional_base<T>::cast_ptr(const 
boost::optional_detail::optional_base<T>::internal_type 
*,boost::optional_detail::optional_base<T>::is_not_reference_tag) const' 
: cannot convert parameter 2 from 'boost::integral_constant<bool,true>' 
to 'boost::optional_detail::optional_base<T>::is_not_reference_tag'

         with

         [

             T=std::vector<double> &

         ]

         and

         [

             T=std::vector<double> &

         ]

         No constructor could take the source type, or constructor 
overload resolution was ambiguous

         c:\code\boost\optional\optional.hpp(371) : while compiling 
class-template member function 
'boost::optional_detail::optional_base<T>::pointer_type 
boost::optional_detail::optional_base<T>::get_ptr_impl(void)'

         with

         [

             T=std::vector<double> &

         ]

         c:\code\boost\optional\optional.hpp(407) : see reference to 
class template instantiation 'boost::optional_detail::optional_base<T>' 
being compiled

         with

         [

             T=std::vector<double> &

         ]

c:\code\Networks\Computations\CppComputations\Forecasting\auto_DFS_2_00_computation.cpp(16) 
: see reference to class template instantiation 'boost::optional<T>' 
being compiled

         with

         [

             T=std::vector<double> &

         ]

Joe Gottman