Le 25/01/12 13:26, Stewart, Robert a écrit :
Vicente J. Botet wrote:
Le 24/01/12 22:51, Beman Dawes a écrit :
What do others think? Should /boost/detail/scoped_enum_emulation.hpp functionality be moved to config?
Are there any improvements that would make the emulation better, without turning something simple into something complex? I'm working with a different emulation which uses classes. For example
// enum class cv_status; BOOST_DECLARE_STRONG_ENUM_BEGIN(cv_status) { no_timeout, timeout }; BOOST_DECLARE_STRONG_ENUM_END(cv_status)
The macros are defined as follows:
#ifdef BOOST_NO_SCOPED_ENUMS #define BOOST_DECLARE_STRONG_ENUM_BEGIN(x) \ struct x { \ enum enum_type
#define BOOST_DECLARE_STRONG_ENUM_END(x) \ enum_type v_; \ inline x() {} \ inline x(enum_type v) : v_(v) {} \ inline operator int() const {return v_;} \ friend inline bool operator ==(x lhs, int rhs) \ {return lhs.v_==rhs;} \ friend inline bool operator ==(int lhs, x rhs) \ {return lhs==rhs.v_;} \ friend inline bool operator !=(x lhs, int rhs) \ {return lhs.v_!=rhs;} \ friend inline bool operator !=(int lhs, x rhs) \ {return lhs!=rhs.v_;} \ };
#define BOOST_STRONG_ENUM_NATIVE(x) x::enum_type #else // BOOST_NO_SCOPED_ENUMS #define BOOST_DECLARE_STRONG_ENUM_BEGIN(x) enum class x #define BOOST_DECLARE_STRONG_ENUM_END(x) #define BOOST_STRONG_ENUM_NATIVE(x) x #endif // BOOST_NO_SCOPED_ENUMS
While this is not yet a complete emulation of scoped enums, it has the advantage of that there is no need to use a macro to name the strong type. It looks decent, but shouldn't int be a computed type based upon the size and signed-ness of enum_type? Of course, you could also provide macros to specify the underlying type and use that, instead of enum_type, as the type of v_. That would increase compatibility with strongly typed enums in C++11. The implicit underlying type is int. And yes, another set of macros could be provided to allow to specify the underlying type.
Why convert implicitly to int rather than to enum_type? You could convert to the computed type I mentioned above, but converting to enum_type would ensure the most appropriate conversions, wouldn't it? The conversion operator should be explicit and to the underlying type, which is int. I have to change it to use explicit conversion when the compiler supports it.
It might also be good to put the semicolon closing the enumerated type definition into the _END macro. That would increase symmetry and more strongly tie the _END macro to the construct:
BOOST_DECLARE_STRONG_ENUM_BEGIN(cv_status) { no_timeout, timeout } BOOST_DECLARE_STRONG_ENUM_END(cv_status) Yes, this is better.
It would be nice if the macros would produce strongly typed enums, when available, and devolve to emulation when not. Have you miss the else part?
#else // BOOST_NO_SCOPED_ENUMS #define BOOST_DECLARE_STRONG_ENUM_BEGIN(x) enum class x #define BOOST_DECLARE_STRONG_ENUM_END(x) #define BOOST_STRONG_ENUM_NATIVE(x) x #endif // BOOST_NO_SCOPED_ENUMS
It might also prove useful to have a macro to forward declare them: BOOST_FORWARD_DECLARE_STRONG_ENUM(name). That would forward declare a normal class, when emulating, and forward declare the enum class otherwise.
Yes, this can be useful also. Next follows the new macros with the sugested improvements #ifdef BOOST_NO_SCOPED_ENUMS #define BOOST_DECLARE_STRONG_ENUM_UT_BEGIN(NT, UT) \ struct NT { \ typedef UT underlying_type; \ enum enum_type #ifndef BOOST_NO_EXPLICIT_CONVERSION_OPERATORS #define BOOST_DECLARE_STRONG_ENUM_UT_END(NT) \ ; \ underlying_type v_; \ inline NT() {} \ inline NT(enum_type v) : v_(v) {} \ inline underlying_type underlying() const {return v_;} \ inline explicit operator underlying_type() const {return underlying();} \ }; #else #define BOOST_DECLARE_STRONG_ENUM_UT_END(NT) \ ; \ underlying_type v_; \ inline NT() {} \ inline NT(enum_type v) : v_(v) {} \ inline underlying_type underlying() const {return v_;} \ inline operator underlying_type() const {return underlying();} \ }; #endif #define BOOST_DECLARE_STRONG_ENUM_BEGIN(NT) \ BOOST_DECLARE_STRONG_ENUM_UT_BEGIN(NT,int) #define BOOST_DECLARE_STRONG_ENUM_END(NT) \ BOOST_DECLARE_STRONG_ENUM_UT_END(NT) #define BOOST_STRONG_ENUM_NATIVE(NT) NT::enum_type #define BOOST_FORWARD_DECLARE_STRONG_ENUM(NT) struct NT #else // BOOST_NO_SCOPED_ENUMS #define BOOST_DECLARE_STRONG_ENUM_UT_BEGIN(NT,UT) enum class NT:UT #define BOOST_DECLARE_STRONG_ENUM_UT_END(NT) ; #define BOOST_DECLARE_STRONG_ENUM_BEGIN(NT) enum class NT #define BOOST_DECLARE_STRONG_ENUM_END(NT) ; #define BOOST_STRONG_ENUM_NATIVE(NT) NT #define BOOST_FORWARD_DECLARE_STRONG_ENUM(NT) enum class NT #endif // BOOST_NO_SCOPED_ENUMS Thanks for the suggestions. Vicente