set_chain.rb

module SetChain
  NONDESTRUCTIVE = false

  # Usage:
  # foo.set_chain [:transaction, :response, :result, :score], [Transaction.new, ResponseType.new, Result.new, "42"]
  # foo.transaction.response.result.score # => "42"
  def set_chain(fields, values, destructive = true)
    fields.zip(values).inject(self) do |member, (field, value)|
      setter = "#{field}="
      if destructive
        member.send setter, value
        value
      else
        existing = member.send field
        if member.send(field).nil?
          member.send setter, value
          value
        else
          existing
        end
      end
    end
  end
end

class Object
  include SetChain
end