Re: [boost] problems with binary variant visitors in 1.31

From: Brian McNamara (lorgon_at_[hidden])
Date: 2004-02-06 05:50:43

I haven't tried any of this code, but I just happened to notice this
while glancing...

On Fri, Feb 06, 2004 at 02:29:53AM -0800, E. Gladyshev wrote:
...
> struct my_type
> {
...
>     var d_;
>     
>     template< typename U >
>     void visit( test1& t, U& u )   //test1 doesn't have set()
>     {
>     }
>     
>     template< typename T, typename U >      
>     void visit( T& t, U& u )
>     {
>         t.set(u);
>     }
>     
>     const var& data() const { return d_; }
> };
> 
> main()
> {
>     my_type t1, t2;
>     
>     binary_variant_visitor<my_type> v(t1);
>     ::boost::apply_visitor(v, t1.data(), t2.data() );
> }
> 
> If I change the last line to
>   ::boost::apply_visitor(v, t1.d_, t2.d_ );
> 
> it works fine on both compilers.

data() returns a "const &", whereas I think .d_ will be non-const.  
Offhand I am kinda surprised that any of the visit() methods (which all
want non-const) end up matching, but I have not studied the code very
deeply.

In any case, maybe adding a
>     var& data() { return d_; }
in addition to
>     const var& data() const { return d_; }
will help.

-- 
-Brian McNamara (lorgon_at_[hidden])