Re: [Boost-users] Need help with boost.variant and apply_visitor method overloading.

From: Jiri Palecek (jpalecek_at_[hidden])
Date: 2008-03-28 11:13:50

On Fri, 28 Mar 2008 07:56:59 -0000, Kevin Scarr <kscarr_at_[hidden]>  
wrote:

> I am trying to implement a system for ensuring producers and consumers
> agree on the data type they are exchanging.
>
> However, I also have "general" containers which can send or receive
> anything (mainly routing components).
>
> Anyway, I have tried to setup the following code to implement this
> scheme, however When I compile code (on MSVC 2005), I see the following
> error:
>
> Error	1	error C3066: there are multiple ways that an object of this type
> can be called with these arguments; unable to recover from previous
> error(s); stopping compilation
> c:\boost-1_34_1\boost\variant\detail\apply_visitor_binary.hpp	63	
>
>
> I have tracked it down to the first two overloads where I am trying to
> connect a consumer/producer of a specific type to a general
> producer/consumer.
>

At the first glance (i haven't looked at it thoroughly), the call

   your_visitor(G2Consumer<DataTypes>*, G2Producer<DataTypes>*)

is really ambiguous (the first two overloads are the best matches and none  
of them better than the other). Just add this overload and things should  
work.

Regards
     Jiri Palecek

>
>
> typedef boost::variant<t1*,t2*,t3*> DataTypes;
>
> typedef boost::variant<
>               G2Consumer<t1>*,
>               G2Consumer<t2>*,
>               G2Consumer<t3>*,
>               G2Consumer<DataTypes>* > G2ConsumerTypes;
>
> typedef boost::variant<
>               G2Producer<t1>*,
>               G2Producer<t2>*,
>               G2Producer<t3>*,
>               G2Producer<DataTypes>* > G2ProducerTypes;
>
>
> class doConnectConsumerToProducer : public static_visitor<>
> {
>    public:
//add:
       void operator() ( G2Consumer<DataTypes>* consumer,
                         G2Producer<DataTypes>* producer ) const;

>      template<typename T>
>      void operator() ( G2Consumer<DataTypes>* consumer,
>                        G2Producer<T>*         producer ) const
>      {
>        consumer->RegisterAsConsumer( *producer );
>      }
>
>      template<typename T>
>      void operator() ( G2Consumer<T>*         consumer,
>                        G2Producer<DataTypes>* producer ) const
>      {
>        consumer->RegisterAsConsumer( *producer );
>      }
>
>      template<typename T>
>      void operator() ( G2Consumer<T>* consumer,
>                        G2Producer<T>* producer ) const
>      {
>        consumer->RegisterAsConsumer( *producer );
>      }
>
>      template<typename C, typename P>
>      void operator() ( G2Consumer<C>* consumer,
>                        G2Producer<P>* producer ) const
>      {
> 	G2Base* c = dynamic_cast<G2Base*>(consumer);
> 	G2Base* p = dynamic_cast<G2Base*>(producer);
>
>          std::ostringstream msg;
>
>          msg << "Incompatible consumer(" << typeid(*c).name()
>              << ") and producer(" << typeid(*p).name()
>              << ") types" << std::ends;
>
>          throw G2::exception( msg.str().c_str() );
>      }
> };
>
> // Helper function to drive this above.
> void connectConsumerToProducer( G2ConsumerTypes& c, G2ProducerTypes& p )
> {
>    apply_visitor( doConnectConsumerToProducer(), c, p );
> }

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