Joe Gottman wrote:
In order to avoid having an unnamed namespace inside a header file, none.hpp has been rewritten as
namespace boost { none_t const none = ((none_t)0) ; } // namespace
But if two source files contain none.hpp won't this violate the one-definition rule?
none would have internal linkage according to 7.1.5.1/2. So it wouldn't violate the ODR. But a pointer to none from one translation unit would differ from a pointer to none from a different TU.
What's wrong with defining none_t and none as follows:
namespace boost { enum none_t {none = 0}; }
This allows us to have a unique value boost::none of type boost::none_t that can be included in any number of source files without violating the ODR.
It would also avoid the pointer-to-none problem mentioned above, simply because you can't create a pointer to an enumerator. However, none_t instances of enumeration type would be implicitely convertible to int, while the member pointer version of none_t isn't. Regards, m Send instant messages to your online friends http://au.messenger.yahoo.com