Version vector class

version_vector.rb

class VersionVector
  # D. S. Parker, et al. Detection of Mutual Inconsistency in
  # Distributed Systems. IEEE Trans. Softw. Eng. 9, 3 (May 1983), 240-247.

  def initialize
    @versions = {}
    @versions.default = 0
  end

  def [](site)
    @versions[site]
  end

  def increment(site)
    @versions[site] += 1
  end

  def sites
    @versions.keys
  end

  protected :sites

  def to_s
    @versions
  end

  def equals?(other)
    sites = (self.sites + other.sites).uniq
    not (sites.collect{ |site| self[site] == other[site] }.include? false)
  end

  alias :== :equals?

  def dominates?(other)
    sites = (self.sites + other.sites).uniq

    # Every version in the first vector must be greater than or equal to the
    # corresponding version in the second
    not (sites.collect{ |site| self[site] >= other[site] }.include? false) and
    # At least one version in the first vector must be greater than the
    # corresponding version in the second
    (sites.collect{ |site| self[site] > other[site] }.include? true)
  end

  def compatible?(other)
    equals?(other) || dominates?(other) || other.dominates?(self)
  end

  def conflicts?(other)
    !compatible?(other)
  end
end