Re: [boost] Typesafe enums proposal

From: Sebastien Martel (smartel_at_[hidden])
Date: 2005-06-17 11:18:29

Maksym Motornyy wrote:

Is there a way to integrate a solution to this problem :

[google groups] http://tinyurl.com/dtnx3

-seb

> Hello, all.
> 
> I want to propose typesafe enums. Sources are available in Boost Sandbox 
> (typesafe_enums.zip). Were tested under VC 7.1.
> 
> Main features are:
> - type safety;
> - meaningful printable names;
> - ability to use in switch-case constructs;
> - iteration through enumerators;
> - enumerator-specific methods;
> 
> Basic usage
> ===========
> 
> class season_policy: public boost::simple_enumeration_policy
> {
> public:
>      BOOST_DEFINE_ENUMERATOR( WINTER )
>      BOOST_DEFINE_ENUMERATOR( SPRING )
>      BOOST_DEFINE_ENUMERATOR( SUMMER )
>      BOOST_DEFINE_ENUMERATOR( AUTUMN )
> 
>      typedef boost::mpl::vector< WINTER, SPRING, SUMMER, AUTUMN > 
> enumerators;
> };
> 
> typedef boost::enumeration< season_policy > season;
> 
> Type safety
> -----------
> 
> season s = season::WINTER();
> 
> if ( s ) // accidentally forgotten comparison, wouldn't compile
>      BOOST_ASSERT( false );
> 
> if ( s == season::SUMMER() )
>      std::cout << "Let's go in for fishing!";
> 
> Meaningful printable names
> --------------------------
> 
> season s = season::WINTER();
> BOOST_CHECK_EQUAL( s->get_name(), "WINTER" );
> 
> Ability to use in switch-case constructs
> ----------------------------------------
> 
> season s = season::SUMMER();
> 
> switch ( s.get_id() )
> {
> case BOOST_ENUMERATOR_ID( season, SUMMER ):
>      break;
> default:
>      BOOST_ERROR( "Should not fall here." );
>      break;
> }
> 
> Iteration through enumerators
> -----------------------------
> 
> for ( season::iterator i = season::begin(); i != season::end(); ++i )
>      std::cout << ( *i )->get_name() << " ";
> 
> Advanced usage
> ==============
> 
> class operation_policy
> {
> public:
>      class base_enumerator
>      {
>      public:
>          virtual double eval(
>              double operand1, double operand2 ) const = 0;
>      };
> 
>      template < typename Functor >
>      class enumerator_impl: public base_enumerator
>      {
>      public:
>          double eval( double operand1, double operand2 ) const
>          {
>              return Functor()( operand1, operand2 );
>          }
>      };
> 
>      class PLUS: public enumerator_impl< std::plus< double > >
>      {
>      };
> 
>      class MINUS: public enumerator_impl< std::minus< double > >
>      {
>      };
> 
>      class TIMES: public enumerator_impl< std::multiplies< double > >
>      {
>      };
> 
>      class DIVIDE: public enumerator_impl< std::divides< double > >
>      {
>      };
> 
>      typedef boost::mpl::vector<
>          PLUS, MINUS, TIMES, DIVIDE > enumerators;
> };
> 
> typedef boost::enumeration< operation_policy > operation;
> 
> Enumerator-specific methods
> ---------------------------
> 
> for ( season::iterator i = season::begin(); i != season::end(); ++i )
>      std::cout << ( *i )->eval( 4, 2 ) << " ";
> // expected output is: 6 2 8 2
> 
> Is anybody found it useful?
> 
> Sincerely,
> Maksym Motornyy.
> 
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