[Python-ideas] IntFlags

[Neil Girdhar]

FYI:

ctypes already has a BitFlags/BitFields mechanism.

class Flags_bits(ctypes.LittleEndianStructure):
    _fields_ = [
            ("logout", c_uint8, 1),
            ("userswitch", c_uint8, 1),
            ("suspend", c_uint8, 1),
            ("idle", c_uint8, 1),
        ]


On Thu, Mar 5, 2015 at 11:26 PM, Neil Girdhar <mistersheik at gmail.com> wrote:

> Even if you constrain yourself to the BitFlags rather than the more
> general BitFields, I strongly disagree with the interface that people are
> proposing involving & and ~ operators.  In general, good interface design
> reflects the way we think about objects — not their underlying
> representation.  The fact is that a BitSet's main operations are set and
> clear individual bits.  It is as if the BitFlags are a namedtuple with
> Boolean elements whose underlying storage happens to be an integer.
> Therefore, the interface that makes the most sense is member access:
>
> my_bit_flags.some_bit = True
> my_bit_flags.some_bit = False
>
> I don't see the justification for writing these as
>
> my_bit_flags |= TheBitFlagsClass.some_bit
> my_bit_flags &= ~TheBitFlagsClass.some_bit
>
> The second line is particularly terrible because it exposes you to making
> mistakes like:
>
> my_bit_flags &= TheBitFlagsClass.some_bit
> my_bit_flags |= ~TheBitFlagsClass.some_bit
>
> — both of which are meaningless.
>
> It also makes it hard to convert code between the alternate implementation
> of using a namedtuple.  It should be easy to do that in my opinion.
>
> Best,
>
> Neil
>
> On Thu, Mar 5, 2015 at 12:57 PM, Serhiy Storchaka <storchaka at gmail.com>
> wrote:
>
>> On 05.03.15 19:29, Neil Girdhar wrote:
>>
>>> Have you looked at my IntFields generalization of IntFlags?  It seems
>>> that many of your examples (permissions, e.g.) are better expressed with
>>> fields than with flags.
>>>
>>
>> It looks too complicated for such simple case. And it has an interface
>> incompatible with plain int.
>>
>>
>>
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