From: "David A. Black" <dblack@...>
Date: 2009-01-29T11:21:33+09:00
Subject: Re: Bitwise question

On Thu, 29 Jan 2009, Pascal J. Bourguignon wrote:

> Rob Biedenharn <Rob@AgileConsultingLLC.com> writes:
>
>> On Jan 28, 2009, at 4:32 PM, Pascal J. Bourguignon wrote:
>>
>>> Andrew Barringer <abarringer@bsecure.com> writes:
>>>
>>>> What's the best way to find out if user has access to all requested
>>>> permissions?
>>>
>>> (def check(permissions,bits)
>>>  (bits . inject(true) { | r , b |
>>>                    (r and (0 != (permissions & (1 << b))))
>>>                 })
>>> end)
>>>                                                                                              nil
>> Or a simpler version:
>>
>> class Integer
>>    def as_bits
>>      ary = []
>>      (self.size*8).times {|i| ary.unshift(i) if self[i].nonzero?}
>>      ary
>>    end
>>
>>    def check_permissions(*bits)
>>      bits.all? {|bit| self[bit].nonzero? }
>>    end
>> end
>
> Simplier?  A class, two methods, a lot of operations, a lot of memory!

as_bits is just there to provide information for the sake of
understanding the examples. check_permissions is Rob's answer to the
original question. It looks about as simple as it could be: very
idiomatic, clear, and concise.

If you don't like adding to Integer you can make it functional-style
by adding a second argument.


David

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