class Date

If no +config.beginning_of_week+ was specified, returns +:monday+.
If Date.beginning_of_week has not been set for the current request, returns the week start specified in config.beginning_of_week.
Returns the week start (e.g. +:monday+) for the current request, if this has been set (via Date.beginning_of_week=).

def beginning_of_week
  ::ActiveSupport::IsolatedExecutionState[:beginning_of_week] || beginning_of_week_default || :monday
end