class Date

def beginning_of_week=(week_start)

:monday, :tuesday, :wednesday, :thursday, :friday, :saturday, :sunday
This method accepts any of the following day symbols:

Sets Date.beginning_of_week to a week start (e.g. :monday) for current request/thread. 
def beginning_of_week=(week_start)
  Thread.current[:beginning_of_week] = find_beginning_of_week!(week_start)
end