Re: [boost] Interest in bit-wise flags?

Subject: Re: [boost] Interest in bit-wise flags?
From: Jeffrey Bush (jeff_at_[hidden])
Date: 2014-06-19 02:07:02

> 
> Hi Boost!
> 
> I have developed a type-safe bit-wise flags class for my own personal use
> and
> am wondering if it would be of interest for me to submit it as a Boost
> library.
> At the moment it is not ready for submission (code is messy) but I am
> testing
> the waters so I present an overview below.
> * Fully ISO standard C++11 (except for an MSVC version which is
> API-compatible
>   except it doesn't support as many an infinite number of flag names)
> * They are type-safe, requiring explicit casts to and from 
integers/booleans
> * Supports standard bit-wise operations, and always keep values within the
>   possible set of flags
> * Supports getting the name of a flag and looking up flags by name at
> run-time
>   (when a flag is actually multiple-flags it gives something like "A|B")
> * Supports getting an array of all flags at run-time
> 
> Now the bad things, which may be a deal-breaker:
> * Because of limitations in C++ the syntax can feel a bit awkward. You 
have
> to
>   use a macro to define flag-names (which actually creates a class) then 
you
>   can pass those flag-names as template arguments to the flags. An 
example:
>     FLAG_NAME(A);
>     FLAG_NAME(B);
>     FLAG_NAME(C);
>     typedef Flags<std::uint8_t, Flag_A, Flag_B, Flag_C>::WithValues<0x01,
> 0x02, 0x04> MyFlags;
> * I also couldn't get around using the ::WithValues nested class
> * I use a set of macros to make this cleaner (e.g. the above could be
>   FLAGS(A, B, C)) and once defined there is no more ugliness
> 
> Thanks for consideration!
> Jeff
> 
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Jeffrey Bush <jeff <at> coderforlife.com> writes:

I have posted the current (ugly) code online: 
https://gist.github.com/coderforlife/6d8bac451d49dd1a0c81#file-flags-hpp

Above that is the even uglier MSCV-specific implementation.

I focused on function not readability when making it, I understand that it 
would take significant work to make it Boost ready.

Differences from BOOST_BITMASK or lordodinscpplib are that it supports ~ 
that is value-constrained (only flips bits that are covered by flags, it 
supports names at run-time (converting to and from strings), and it can 
default-value then flags with powers of two.

If those features are undesired, then this class is unnecessary seeing that 
those other solutions are significantly simpler or more portable.

However, looking at those has given me some ideas on how to simplify my code 
and make it possibly work in Clang.

Jeff