hash_set_extension.rb

class Hash
  alias_method :+, :merge

  def -(other)
    other_keys = Set.new(other.keys)

    # Irrelevant value method
    # reject { |k, _v| other_keys.include?(k) }

    # Relevant value method
    reject { |k, v| other_keys.include?(k) && other[k] == v }    
  end

  def intersection(other)
    intersecting_keys = self.keys & other.keys

    # Irrelevant value method
    # self.slice(*intersecting_keys)

    # Relevant value method
    select { |k, v| intersecting_keys.include?(k) && other[k] == v }
  end

  alias_method :&, :intersection

  def exclusive_intersection(other)
    # Does potentially odd things when values are relevant
    (self + other) - (self & other)
  end

  alias_method :^, :exclusive_intersection
end