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BanditMask provides a generic wrapper for working with bitmasks.


Add this line to your application's Gemfile:

gem 'banditmask'

And then execute:

$ bundle

Or install it yourself as:

$ gem install banditmask



Create a class which inherits from BanditMask, and declare the available bit names and their corresponding values.

class ChmodMask < BanditMask
  bit :read,    0b001
  bit :write,   0b010
  bit :execute, 0b100

ChmodMask.bits # => { :read => 1, :write => 2, :execute => 4 }

Instantiate a new mask class:

mask =
# or
current_bitmask = 0b001 | 0b010
mask = current_bitmask

Enable bits by name.

mask << :read << :execute

Ask whether specific bits are enabled.

mask.include? :read           # => true
mask.include? :write          # => false
mask.include? :execute        # => true
mask.include? :read, :write   # => false
mask.include? :read, :execute # => true

Retrieve a list of all currently enabled bits.

mask.bits # => [:read, :execute]


In a class with a bitmask attribute, extend BanditMask::Banditry and call BanditMask::Banditry.bandit_mask to add accessor methods for working with the bitmask attribute.

class ObjectWithBitmaskAttribute
  attr_accessor :bitmask

  extend BanditMask::Banditry
  bandit_mask :bitmask, as: :bits, with: ChmodMask

obj =
obj.bitmask = 0b011

This gives you a reader method which delegates to BanditMask#bits.

obj.bits # => [:read, :write]

It also gives you a writer method which lets you overwrite the bitmask.

obj.bits = [:read, :execute]
obj.bitmask # => 5

Finally, it gives you a query method for checking whether particular bits are set on the bitmask.

obj.bits? :read           # => true
obj.bits? :write          # => false
obj.bits? :execute        # => true
obj.bits? :read, :write   # => false
obj.bits? :read, :execute # => true


After checking out the repo, run bin/setup to install dependencies. Then, run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release to create a git tag for the version, push git commits and tags, and push the .gem file to


  1. Fork it ([my-github-username]/banditmask/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request