Is flags enum needed in Phobos?

[Denis Shelomovskij]

26.09.2012 21:52, Dmitry Olshansky пишет:
> On 26-Sep-12 21:39, Denis Shelomovskij wrote:
>> 25.09.2012 21:14, Denis Shelomovskij пишет:
>>> .NET has FlagsAttribute, Java has EnumSet. Looks like we need this too.
>>> How about to add a library solution to Phobos?
>>>
>>> My variant is here (search for `flagEnum`):
>>> https://bitbucket.org/denis_sh/misc/src/tip/stdd/typecons.d
>>>
>>> It has a bug and I have no idea how to fix it:
>>> `AB.init |= AB.a` and `AB.a |= AB.a` are allowed.
>>> (no, we can't make `AB.a` const to disallow the second case because it
>>> will disallow this: `auto a = AB.a; a |= AB.a;`)
>>>
>>> Also I'm not sure:
>>> * Should we support converting from a number to a flag enum?
>
> I'd suggest an explicit way to do so. Like to!(flagEnum) or a standalone
> helpers.
>
>>> * If so, should we support values not from enum flags or throw
>>> exceptions (it may be configurable)?
> If to! is used I guess throw exceptions if it doesn't fit.
>
>>> * Is `flagEnum` an appropriate name?
>
> Since it's a type (right?) I'd think EnumFlag, FlagSet or even Java's
> EnumSet. Generally I think I like words 'set' and/or 'flag' in the name.
>
>> OK. Looks like such functionality isn't needed and I don't have to do a
>> pull request. What about to close
>> http://d.puremagic.com/issues/show_bug.cgi?id=6946
>> with WONTFIX?
>>
> First, calm down. Second, I, for one, like it.

Thanks for the answer, but still there are only few guys here 
interesting in it to be included in Phobos, so WONTFIX-ing the issue 
looks reasonable. I can just support this struct in my library for you.

> The place to go is most likely std.bitmanip or std.typecons. I haven't
> looked much at the actual code but the usage seems straightforward.
>
> Another thought is to generalize it to something beyond 1-bit flags. How
> about packing various flags (set of 3-state flag, 4-state flag  etc.) in
> one fixed struct?

Please give me usage examples (unittests), and I will implement the 
functionality. Now I don't understand what are n-state flags and what is 
the difference with std.bitmanip.bitfields.

-- 
Денис В. Шеломовский
Denis V. Shelomovskij