ActiveSupport、Time#end_of_week, Time#at_end_of_week
>> require "rubygems" => true >> require "active_support" => true >> Time.local(2008, 12, 31).end_of_week => Sun Jan 04 23:59:59 +0900 2009 >> Time.local(2008, 12, 31).at_end_of_week => Sun Jan 04 23:59:59 +0900 2009