Re: [boost] Re: generalization of types in variant

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-10-28 14:33:48

--- "E. Gladyshev" <egladysh_at_[hidden]> wrote:
[...]
> Oh, I think I know what you mean.
> 
> struct visitor
> {
>   template< typename T >
>   operator()( T& x )
>   {
>     x.f();
>   };
>   operator()( boost::empty& ) {}
> };
> 
> It becames even more interesting for binary visitors.
> All your visitors will need boost::empty overloads
> and you would have to make sure that you are not
> using types any other non-throw types to do 
> the optimization trick.
> 
> struct visitor
> {
>   template< typename T, typename U >
>   operator()( T& x, U& u )
>   {
>     x.f( u );  //general function
>   };
>   //optimization stuff
>   template<typename U> operator()( boost::empty&, U& );
>   template<typename T> operator()( T&, boost::empty& );
>   void operator()( boost::empty&, boost::empty& );
> };

After thinking about it, I doubt that the compiler
will able to resolve the above overloads for 
binary visitors.

For example,

visitor v;
int x;
boost::empty y;
v( x, y ); //error: unresolved overloads

If this is true, then overloads is not a solution.
I do use binary overloads in my code.

Eugene

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