class RuboCop::AST::NodePattern::Compiler

def unify_in_union(enum)
  # We need to reset @unify before each branch is processed.
  # Moreover we need to keep track of newly encountered wildcards.
  # Var `new_unify_intersection` will hold those that are encountered
  # in all branches; these are not a problem.
  # Var `partial_unify` will hold those encountered in only a subset
  # of the branches; these can't be used outside of the union.
  return to_enum __method__, enum unless block_given?
  new_unify_intersection = nil
  partial_unify = []
  unify_before = @unify.dup
  result = enum.each do |e|
    @unify = unify_before.dup if new_unify_intersection
    yield e
    new_unify = @unify.keys - unify_before.keys
    if new_unify_intersection.nil?
      # First iteration
      new_unify_intersection = new_unify
    else
      union = new_unify_intersection | new_unify
      new_unify_intersection &= new_unify
      partial_unify |= union - new_unify_intersection
    end
  end
  # At this point, all members of `new_unify_intersection` can be used
  # for unification outside of the union, but partial_unify may not
  forbid_unification(*partial_unify)
  result
end