Ruby utility for parsing bitmask options.

bitmask.rb

# Usage:
#  Bitmask[:list, :of, :option, :keys, value]
# where the last key in the list will be represented by the least significant
# bit in value.
#
# Example:
#  Bitmask[:optionA, nil, :optionB, :optionC, 0b1010]
#  #=> {:optionA=>true, :optionB=>true, :optionC=>false}
# Use nils to indicate bits that do not have a meaning.
class Bitmask
  def self.[](*fields, bitmask)
    unless bitmask.is_a? Integer
      raise ArgumentError,
            "A bitmask can only be an Integer, #{bitmask.class} given"
    end

    Hash[
      fields.map.with_index(1) do |field, bit|
        next unless field
        [field, bitmask & (1 << fields.size - bit) > 0]
      end.compact
    ]
  end
end