class Roda::RodaPlugins::TypecastParams::Params

def subkey(keys, do_raise)
  unless key = keys.shift
    return self
  end
  reason = :invalid_type
  case key
  when String
    unless @obj.is_a?(Hash)
      raise Error, "parameter #{param_name(nil)} is not a hash" if do_raise
      return
    end
    present = !@obj[key].nil?
  when Integer
    unless @obj.is_a?(Array)
      raise Error, "parameter #{param_name(nil)} is not an array" if do_raise
      return
    end
    present = key < @obj.length
  else
    raise ProgrammerError, "invalid argument used to traverse parameters: #{key.inspect}"
  end
  unless present
    reason = :missing
    raise Error, "parameter #{param_name(key)} is not present" if do_raise
    return
  end
  self[key].subkey(keys, do_raise)
rescue => e
  handle_error(key, reason, e)
end