Re: [boost] none.hpp

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2006-07-25 09:29:46

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?  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.
> 
Hi Joe,

Sorry I couldn't respond earlier (having two jobs is killing me, 
although  I can't say I don't enjoy it at the end of the month ;)

As Martin said the problem with an enum is that it isn't type-safe, and 
in the particular case of optional<> that is very important because '0' 
is a "valid" value (so it's much more important than with a smart pointer)

Fernando Cacciola