Re: [boost] Re: How To Declare Enumerators (was: IOStreamsformalreviewstart)

From: Rob Stewart (stewart_at_[hidden])
Date: 2004-09-13 11:38:20

From: "Noah" <noah_at_[hidden]>
> 
> I hate having the shift value represent the flag - it's too easy to believe
> that you're just supposed to pass the value as is.  Then you have to go
> lookup whether the value is a shift or the flag value itself.  It's a
> serious pain.

I don't understand what you mean.  I've never been confused when
using left shift to generate the enumerator-definition.

> You could have the best of both worlds if you wrap the parameter up in a
> class.  Here's a brief sketch off the top of my head (so don't try to
> compile and use it!):
> 
> template<typename E>
> class BitFlag
> {
> 	int flag;
> 
> public:
>     BitFlag(E val)
> 	{ flag = 1 << val; }
> };
> 
> It makes the enum much easier to deal with since you can just simply put the
> flags in a list and not worry about explicitly initializing each flag.  You
> can also add additional functionality.  You could overload operators to
> handle passing or masking multiple flags.  You could also, through the use
> of a traits class, validate flag combinations.

However wonderful that could be, the fact is that an
enumerator-definition must be a constant-expression.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;