[boost] [C++0x] Emulation of scoped enums

Subject: [boost] [C++0x] Emulation of scoped enums
From: Beman Dawes (bdawes_at_[hidden])
Date: 2009-03-05 10:37:12

The improved type safety of the C++0x scoped enum feature is attractive, 
so I'd like to start using it as it becomes available in compilers.

See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf 
for a description. Note that the committee changed the name from 
strongly typed enums to scoped enums.

See the attached for a boost/detail header that provides macro wrappers 
that use scoped enums if available, otherwise fall back on C++03 
namespaces and unscoped enums. It lets a library write:

   BOOST_SCOPED_ENUM_START(algae) { green, red, cyan };
     BOOST_SCOPED_ENUM_END
   ...
   BOOST_SCOPED_ENUM(algae) sample( algae::red );
   void func(BOOST_SCOPED_ENUM(algae));

and then a user can write:

   sample = algae::green;
   func( algae::cyan );

Comments or suggestions appreciated,

--Beman


//  scoped_enum_emulation.hpp  ---------------------------------------------------------//

//  Copyright Beman Dawes, 2009

//  Distributed under the Boost Software License, Version 1.0.
//  See http://www.boost.org/LICENSE_1_0.txt

//  Generates C++0x scoped enums if the feature is present, otherwise emulates C++0x
//  scoped enums with C++03 namespaces and enums. The Boost.Config BOOST_NO_SCOPED_ENUMS
//  macro is used to detect feature support.
//
//  Caution: only the syntax is emulated; the semantics are not emulated and
//  the syntax emulation doesn't include being able to specify the underlying type.
//
//  See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf for a
//  description of the feature. Note that the committee changed the name from
//  strongly typed enums to scoped enums.  
//
//  Sample usage:
//
//     BOOST_SCOPED_ENUM_START(algae) { green, red, cyan }; BOOST_SCOPED_ENUM_END
//     ...
//     BOOST_SCOPED_ENUM(algae) sample( algae::red );
//     void foo( BOOST_SCOPED_ENUM(algae) color );
//     ...
//     sample = algae::green;
//     foo( algae::cyan );

#ifndef BOOST_SCOPED_ENUM_EMULATION_HPP
#define BOOST_SCOPED_ENUM_EMULATION_HPP

#include <boost/config.hpp>

#ifndef BOOST_NO_SCOPED_ENUMS

# define BOOST_SCOPED_ENUM_START(name) enum class name
# define BOOST_SCOPED_ENUM_END
# define BOOST_SCOPED_ENUM(name) name

#else

# define BOOST_SCOPED_ENUM_START(name) namespace name { enum enum_t
# define BOOST_SCOPED_ENUM_END }
# define BOOST_SCOPED_ENUM(name) name::enum_t

#endif

#endif  // BOOST_SCOPED_ENUM_EMULATION_HPP