From: Brian Candler <b.candler@...>
Date: 2008-09-29T17:08:30+09:00
Subject: Re: irb: 1 & 1 => 1, not true    huh?  I thought 1 & 1 => tr

> Bottom line is this: What is Ruby idiom to test for bit mask?  Is there
> a more simple way to write:
> 
> if session[:permissions] & Permissions::SomeMask ==
> Permissions::SomeMask
>   # user has permission to wash clothes, etc.
> end

That's basically right - you can factor this out into your own method if 
you do it a lot.

If you want to test for a single bit, there is Fixnum#[]

a = 14
a[0] # 0
a[1] # 1
a[2] # 1
a[3] # 1
a[4] # 0

You'd still have to test for a[2] == 1, since 0 and 1 are both true.

However you could use a different representation for your permissions, 
such as a string containing a single letter for each permission granted. 
Then:

  if session[:permissions].include?("w")
    # user has permission to wash clothes
  end

or simply

  if session[:permissions]["w"]
    # user has permission to wash clothes
  end
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