Re: [boost] [rfc] small flags library

From: Marat Khalili (0x8.0p15_at_[hidden])
Date: 2007-08-15 14:48:00

Iain Denniston wrote:

>> 1. Is it a generalization of the std::ios_base::flags approach?
> 
> As I understand it std::ios_base::flags will accept any integer - valid 
> or otherwise.

Here in standard library of cygwin gcc 3.4.4 it doesn't.

> My library would be used to prevent invalid integers being 
> passed (though would require valid flags be members of a single enum). 
> Obviously in the case of std::ios_base::flags it would require a rewrite 
> so's the argument would be of type boost::flags<...>

Its argument is <CODE>std::ios_base::fmtflags</CODE> here.

>> 2. It'd be more convenient without <CODE>flags<foo>(...)</CODE> 
>> conversion, wouldn't it?
> 
> [...] if you're passing multiple 
> flags the only way I could think of making it work would be to provide a 
> constructor that accepts integers - which would defeat the purpose of 
> the library. 

Well, I also don't think it is possible with integers, but it is 
possible with flags being not integers like above.

Alternatively, can you make it <CODE>flags(foo_1) | foo2</CODE> (with 
<CODE>flags</CODE> being function) or <CODE>flags | foo_1 | foo2</CODE>?

By the way, why not perform left shift in flags constructor instead of enum?

>> 3. Can <CODE>flags<foo>(foo_1) | foo_2</CODE> be used as a compile-time 
>> constant?
> 
> I'm not sure I entirely understand what you are getting at here - what 
> is it you want to do?

I want it to be usable as a template parameter or switch case. For 
instance, <CODE>class_parametrized_with_iosflags<std::ios_base::dec | 
std::ios_base::left></CODE> will not compile. What about 
<CODE>class_parametrized_with_foo<flags<foo>(foo_1) | foo_2></CODE>?

With Best Regards,
Marat