Re: [boost] interest in a flag library

Subject: Re: [boost] interest in a flag library
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2018-10-26 07:35:28

czw., 25 paź 2018 o 23:28 Masse Nicolas via Boost <boost_at_[hidden]>
napisał(a):

> Hi all,
>
> This is the first time I post on this mailing list :).
> I'm posting because i'd like to know if people would be interested in a
> library to treat enum types as flags. I find that's something which is
> lacking in the language since the introduction of strongly typed enums, and
> I've since written some code in order to do this.
> So far I've seen some discussion on this mailing list about that, but it
> doesn't seems that any library have been written yet.
> So do you think it is worth the effort of porting and documenting my code
> so that it can integrated into boost, or not?
>

Hi. I would use a type-safe library for flags. I am missing one today.
However, given that you provide your own type (which is good IMO), I would
expect a different interface that reflects the meaning more directly. I
consider bit-wise operations to be a hack rather than a proper solution.
Expression `flags & Flags::EXEC` is quite idiomatic, but when I want to
reset a flag, I have to write `flag &=~ Flag::EXEC` (which I call an 'oil
lamp' operator), which is difficult to understand and likely to get wrong.
(In fact, I am not sure I got it right in this example.)

I would rather expect an interface using named functions or indexing
operator:

```
if (!flags[Flag::READ])
  flags.reset(Flag::EXEC);
```

Regards,
&rzej;