[boost] Re: [optional] new assignmet semantic and references

From: Joao Abecasis (jpabecasis_at_[hidden])
Date: 2005-03-01 13:44:14

Fernando Cacciola wrote:
>>Maybe boost::reference_wrapper can be used internally to wrap reference 
>>types and solve this issue.
>>
> 
> How?

I was suggesting the use of reference_wrapper to avoid singling out 
reference types everywhere in the code. The new assignment operators 
might just work.

Anyway, I haven't tested any of this so...

> We're not talking about an implementation problem here; this is about the 
> "correct" behaviour and whether is ok to change to it given the potential 
> impact on user programs.

I see. In that case, please disregard my previous suggestion... I'll 
make a new one, hopefully more helpful ;)

I suggest you document how users may workaround this issue in their code 
using boost::reference_wrapper/ref/cref. Here's a small snippet you can use.

     #include <boost/optional.hpp>
     #include <boost/none.hpp>
     #include <boost/ref.hpp>

     int main()
     {
         int a = 32;
         int b = 1279;

         boost::reference_wrapper<int> ra(a);

         boost::optional<boost::reference_wrapper<int> >
             orw1,                           // default constructor
             orw2(boost::none),              // none_t constructor
             orw3(ra),                       // value constructor
             orw4(boost::ref(a));            // make reference

         boost::optional<int &> ori1(orw1),
             ori2(orw2),
             ori3(orw3.get());

         orw1 = boost::ref(b);
     }

Best regards,

João