----- Original Message ----- From: "Beman Dawes" <bdawes@acm.org> To: <boost@lists.boost.org> Sent: Wednesday, February 11, 2009 4:50 PM Subject: Re: [boost] [filesystem] Version 3 request for comments
In C++0x, the preferred practice for such constants is probably going to be to use a scoped enum:
enum class file_type { status_unknown, file_not_found, regular, directory, symlink, block, character, fifo, socket, type_unknown };
That's a lot more satisfying. We can emulate that approach in C++03 like this:
#ifndef BOOST_NO_SCOPED_ENUM
enum class file_type { status_unknown, file_not_found, regular, directory, symlink, block, character, fifo, socket, type_unknown };
typedef file_type file_type_enum;
#else namespace file_type { enum types { status_unknown, file_not_found, regular, directory, symlink, block, character, fifo, socket, type_unknown }; }
typedef file_type::types file_type_enum; #endif
Is such a scoped enum approach worth taking?
I haven't made up my mind; I'd like to think about it for a few days and also see what could be done to preserve existing code.
Hi, the question is how the user will use these enumerations. if BOOST_NO_SCOPED_ENUM is not defined the user can write file_type e = file_type::file_not_found; which will not evidently compile when defined. How can we force the user to write file_type_enum e = file_type::file_not_found; which is not intuitive, i.e. there is no explicit relation between file_type_enum and file_type. What about making this relation explicit using a metafunction? I'm don't know if the following is clearer enumeration<file_type>::type e = file_type::file_not_found; Best, Vicente __________________________________ #ifndef BOOST_NO_SCOPED_ENUM template <typename E> struct enummeration { typedef E type; }; #else template <typename E> struct enummeration { typedef E::type type; }; #endif #ifndef BOOST_NO_SCOPED_ENUM enum class file_type { status_unknown, file_not_found, regular, directory, symlink, block, character, fifo, socket, type_unknown }; typedef file_type file_type_enum; #else struct file_type { enum type { status_unknown, file_not_found, regular, directory, symlink, block, character, fifo, socket, type_unknown }; } typedef file_type::types file_type_enum; #endif