Re: [boost] unions

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-10-04 12:38:11

Apparently it is me who is missing something.
I've never used it before. What is variant?

Eugene

--- Joel de Guzman <djowel_at_[hidden]> wrote:
> Sounds like a variant to me. What am I missing?
> 
> -- 
> Joel de Guzman
> http://www.boost-consulting.com
> http://spirit.sf.net
> 
> 
> E. Gladyshev <egladysh_at_[hidden]> wrote:
> > Just wondering does boost have something similar to C unions
> > so that you could create heterogenious containers?
> > 
> > Something like the following working pseudo-code
> > 
> > template < typename Types >
> > struct union2
> > {
> >     typedef typename boost::mpl::at_c<Types, 0 >::type type1;
> >     typedef typename boost::mpl::at_c<Types, 1 >::type type2;
> > 
> >     union2() : obj_(0)
> >     {
> >     }
> >     union2( const union2<Types>& l ) : obj_(0)
> >     {
> >         create( l.t_ );
> >         copy( l.obj_ );
> >     }
> >     virtual ~union2()
> >     {
> >         free();
> >     }
> > 
> >     void create( size_t t )
> >     {
> >         free();
> >         t_ = t;
> >         switch( t_ )
> >         {
> >         case 0:
> >             obj_ = new type1;
> >             break;
> > 
> >         case 1:
> >             obj_ = new type2;
> >             break;
> > 
> >         default:
> >             throw;
> >         }
> >     }
> > 
> > private:
> >     size_t t_;
> >     void *obj_;
> >     void free()
> >     {
> >         if( !obj_ ) return;
> >         switch( t_ )
> >         {
> >         case 0:
> >             delete static_cast<type1*>(obj_);
> >             break;
> > 
> >         case 1:
> >             delete static_cast<type2*>(obj_);
> >             break;
> > 
> >         default:
> >             throw;
> >         }
> >         obj_ = 0;
> >     }
> > 
> >     void copy( void* obj )
> >     {
> >         switch( t_ )
> >         {
> >         case 0:
> >             *static_cast<type1*>(obj_) = *static_cast<type1*>(obj);
> >             break;
> > 
> >         case 1:
> >             *static_cast<type2*>(obj_) = *static_cast<type2*>(obj);
> >             break;
> > 
> >         default:
> >             throw;
> >         }
> >     }
> > };
> > 
> > main()
> > {
> >   typedef notus::union2< boost::mpl::vector2<char, short> > my_union;
> > 
> >   std::vector< my_union > gv;
> > 
> >   my_union u(0);
> >   my_union u1(1);
> >   gv.push_back( u );
> >   gv.push_back( u1 );
> > }
> > 
> > 
> > Eugene
> > 
> > 
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